what is the aim of invisible ink experiment

Invisible Ink Reveals Cool Chemistry

A Mad Science Room activity from Crazy Aunt Lindsey

By Lindsey E. Murphy & CrazyAuntLindsey.com

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Key concepts Chemistry Acids Oxidation Heat Introduction Have you ever wondered how spies and secret agents could leave secret messages? Invisible ink might sound high tech, but you can create—and read!—a top secret message with one simple kitchen ingredient: lemons. George Washington's army used this same concept to send secret messages during the American Revolutionary War. What message will you write? Background Lemon juice—and the juice of most fruits, for that matter—contains carbon compounds. These compounds are pretty much colorless at room temperature. But heat can break down these compounds, releasing the carbon. If the carbon comes in contact with the air, a process called oxidation occurs, and the substance turns light or dark brown. Materials •    One half of a lemon (use caution when cutting) •    One half teaspoon of water •    Small bowl •    Spoon •    White paper •    Q-tips •    A lamp with a lightbulb that puts off a lot of heat, such as a 100-watt incandescent bulb or another heat source, such as a radiator •    Optional: Pencil (to write a decoy message on your paper) Preparation •    Squeeze the juice of your lemon half into the bowl. •    Add the water and mix with a spoon. •    Think of a secret message you would like to write—and to whom you're going to deliver it! •    Extra: If you want to be super secret, you can write a boring old message or draw a picture on the paper with a pencil before you write your secret message to disguise it even further. Procedure •    Soak the Q-tip in the lemon juice-and-water solution. •    Use the damp Q-tip to write your top-secret message on the piece of paper. •    Wait a few minutes for the paper to dry. While you're waiting, you can switch on your lamp to give the lightbulb time to heat up (being careful not to touch the hot bulb itself). •    When the paper is dry, hold it up to the hot lamp for a few minutes (but don't let the paper get so hot that it burns). What happened to your invisible ink? How long did it take for the change to occur? •    Extra: Try this activity with other acidic liquids, such as apple juice or vinegar. Which ones work best? Observations and results What happened to your invisible message? What other liquids work well to make invisible ink that develops under heat? When you painted the lemon juice solution onto the paper, the carbon-based compounds were absorbed into the paper's fibers. When you heated the paper, the heat caused some of the chemical bonds to break down, freeing the carbon. Once the carbon came into contact with the air, it went through a process called oxidation, one effect of which is to turn a darker color. Oxidation doesn't always need heat to occur. Some fruits themselves can turn brown from oxidation. Think of an apple or pear slice that is left out on the counter for too long. Cleanup •    Use caution with the lamp, as the lightbulb can stay hot even after it is turned off. •    Have extra lemon solution? Add more water and a little sugar, and you can turn your invisible ink into lemonade! And it's no secret that lemonade tastes good. More to explore " Carbonic Colors: Fizzy, Washable Sidewalk Paint ," from Scientific American and CrazyAuntLindsey.com " Talk through a String Telephone ," from Scientific American " Invisible Ink and More: The Science of Spying in the Revolutionary War ," from Scientific American " Invisible Ink ," from CrazyAuntLindsey.com George Washington, Spymaster: How the Americans Outspied the British and Won the Revolutionary War , by Thomas Allen Amazing Kitchen Chemistry Projects You Can Build Yourself , by Cynthia Light Brown and Blair Shedd This activity brought to you in partnership with CrazyAuntLindsey.com

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Invisible inks

In this experiment, students test a variety of substances to see if they can be used as an invisible ink.

Student Sheet

In this practical I will be:

• Writing messages with a variety of substances which can be used as invisible inks.
• Changing the conditions of the invisible inks to see if messages become visible.
• Using my scientific knowledge to explain how changing the conditions the inks are under affects their visibility. 

Introduction:

It is 410BCE and the Ionian (or Decelean) war, between Athens and Sparta has been raging for four years. You have been tasked by King Agis of Sparta to develop a way of delivering secret messages to his armies, which would be unreadable if they fell into the enemies’ hands. You wonder if there is a way of writing with an ink that is only visible under certain conditions. Like all good science-artists, you decide to investigate further…

Wear eye protection. Wear disposable plastic gloves.

Use one of the methods below to write a question on a piece of white paper. Pass the message to another group who will write an answer to the question and pass it back to you to develop. It would be good to use different types of ink as advised by your teacher. How you reveal the message depends on the ink you used. 

Heat-activated invisible inks

Any of the following for your invisible inks:

• Any acidic fruit juice (e.g. lemon, apple, or orange juice) 
• Onion juice 
• Baking soda (sodium bicarbonate) (or 1 M sodium hydrogen carbonate)
• Vinegar (or 1 M ethanoic acid)
• Dilute cola 
• Diluted honey 
• Soapy water (or 0.1 M sodium carbonate)
• Sucrose (table sugar) solution (1 tsp in 10 cm 3  water)

Other Equipment:

• Iron or oven at 230 °C or hotplate
• A4 paper or filter paper
• Paintbrushes (and/or straws, cotton buds, spills)
• White tiles (For using on the hotplate. The tiles heat up but protect the paper from burning.)
• Use the ink by writing your message with it using a paintbrush, spill, cotton bud, straw with a cut end to make a nib, or toothpick with cloth wrapped around it. Let the message dry in the air or use a hairdryer. 
• Write another (not secret) message on the paper with ballpoint pen, pencil or crayon, so it doesn’t appear to be blank and meaningless. Do not use a fountain pen since this ink could run into your invisible ink and make it visible. Avoid using lined paper to write your invisible message, for the same reason.

Most invisible inks are made visible by heating the paper. Take extra care when heating the paper. An easy way to reveal these types of messages is to iron the paper gently. The paper containing the message can be placed onto a white (ceramic) tile and the white tile can then be placed onto a hotplate. This is a reasonably safe way to heat the paper without risk of burning and it works well to reveal the message.

The paper can also be placed directly onto the hotplate on a low heat but greater care must be taken because it is more likely to burn this way if not supervised carefully.

Going further:

Inks developed by chemical reactions Many of them work as pH indicators, so when in doubt, paint or spray a suspected message with a base (like sodium carbonate solution) or an acid (like lemon juice). 

• Phenolphthalein (pH indicator) HIGHLY FLAMMABLE & HARMFUL, developed by 0.1 M sodium carbonate (Solid is IRRITANT – solution is LOW HAZARD) (or another base).
• Thymolphthalein HIGHLY FLAMMABLE & HARMFUL, developed by 0.1M sodium carbonate (or another base) 
• Vinegar or  1 M acetic (ethanoic) acid, developed by red cabbage water 
• Ammonia(1 M ammonium hydroxide) developed by red cabbage water 
• 1 M sodium hydrogen carbonate sodium bicarbonate (baking soda), developed by grape juice 
• M copper sulfate, developed by 1 M sodium iodide, 0.1 M sodium carbonate, or 1 M ammonium hydroxide 
• 0.005 M lead(II) nitrate TOXIC, developed by 1 M sodium iodide 
• M iron sulfate IRRITANT, developed by 0.1 M sodium carbonate, 1% starch solution (e.g. corn starch or potato starch), or by 0.1 M iodine solution 
• Lemon juice, developed by 0.1 M iodine solution 
• Paintbrushes (and/or straws, cotton buds)
• Use the ink by writing your message with it using a paintbrush, spill, cotton bud, straw with a cut end to make a nib, or toothpick with cloth wrapped around it. Let the message dry in the air or use a hairdryer.
• Write another (not secret) message on the paper with ballpoint pen, pencil, or crayon, so it doesn’t appear to be blank and meaningless. Do not use a fountain pen since this ink could run into your invisible ink and make it visible. Avoid using lined paper to write your invisible message, for the same reason.
• Your message will be developed by spraying, wiping or painting the paper with a second chemical such as an acid. 

Inks developed by ultra-violet light (black light)

• Dilute laundry detergent (the bluing agent glows) or 0.1 M sodium carbonate hydrated (Check packets for safety notes)
• Tonic water (quinine glows) 
• Vitamin B-12 dissolved in vinegar 
• Use the ink by writing your message with it using a paintbrush, spill, cotton bud, straw with a cut end to make a nib, or toothpick with cloth wrapped around it. Let the message dry in the air or use a hairdryer or warm radiator. 
• Messages are revealed by shining an ultraviolet light on the paper.

Some of these are organic substances that oxidize when heated, which usually turns them brown or black because the compounds break down. For this type of “heat fixed” ink, any acidic fluid will work in helping to develop the ink. The most secure way to use any of the following substances for invisible ink is by dilution, usually with water, close to the concentration point when they become difficult to develop. This can only be determined by trial and error.

Inks developed by chemical reactions

In most cases, the substance changes colour when mixed with an acid or base because the pH changes and the liquid acts like an indicator and changes colour. In some cases specific indicators have to be used during which a chemical reaction takes place in which there is a colour change or a precipitate is formed.

Some inks glow faintly or fluoresce when under an ultra-violet lamp. This is a property of many substances, particularly organic substances and body fluids. Other inks work in a near opposite way by absorbing ultra-violet light but without fluorescing. When these are used on fluorescent paper, the inked areas fluoresce less than the surrounding paper area when under an ultra-violet lamp. This is especially a property of inks with a yellow tint. Some UV-visible inks may be detected on a photocopy, due to the relatively strong ultra-violet component in light from the photocopier scanning head.

Teacher and Technician Sheet

In this practical students will:

• Write messages with a variety of substances which can be used as invisible inks.
• Change the conditions of the invisible inks to see if messages become visible.
• Use their scientific knowledge to explain how changing the conditions the inks are under affects their visibility. 

Introduction for teachers:

(This topic could start with a group discussion or a short story woven around the facts given below, during which the teacher introduces the ideas especially the words in bold. This is a fun activity but does have some real chemistry behind it. However, for younger children probably the best are the heat-stimulated inks.)

Invisible ink is any substance that you can use to write a message that is invisible until the ink is revealed. Anyone can write an invisible message, assuming you have paper, because body fluids can be used as invisible ink.

Invisible ink has a history that goes back in time. Ovid (43 BCE-17/18 CE), a Roman poet wrote in his Ars Amatoria in 18BCE:

“Characters written in fresh milk are a well-known means of secret communication. Touch them with a little powdered charcoal and you will read them.”

At the other extreme, Mary, Queen of Scots (1542-1587), used invisible ink and ciphers to communicate with Catholic supporters. Her supporters wrote to her using two common substances: alum (hydrated potassium aluminium sulfate) or gall ink (tannic acid from parasitic wasps in oak trees galls). The alum letters would be developed by soaking the letter in water, and the gall ink would be developed by soaking the letter in iron sulfate solution.

During times of secret love, war or in the world of spies in the cold war, high security is important and there is often the need for invisible ink with which a message can be written, be invisible, and when it reaches the recipient be brought back so it can be seen.

During World War II the Special Operations Executive (SOE) were a group of secret agents operating behind enemy lines. This meant they had to operate without being detected. Hence, messages were often passed using invisible ink. In their training manual the following properties of an ‘ideal’ invisible ink were identified.

• It needs to mix with water so it can be widely used.
• Non-volatile , i.e. no pronounced smell to the ink.
• Must not deposit crystals on the writing paper, i.e. not easily seen in glancing light.
• Be invisible under ultraviolet light .
• Does not decompose or discolour the paper, as with photo paper using silver nitrate.
• Non-reactive with iodine, or with any of the other usual developers.
• Potential developers for the ink should be as few as possible.
• Should not develop under heat .
• Easily obtainable and has at least one plausible innocent use by the holder.
• Not a compound of several chemicals.

SOE agents were trained not to risk their lives so they used invisible inks as a back-up method of communication when other, more secure communication techniques were unavailable. The agency supplied special inks to its field agents. When agents were forced to improvise, they were advised to dilute their invisible ink as much as possible to reduce chances of detection. 

The properties identified by the SOE could be discussed by students as to why they are important criteria for an invisible ink. The students will enjoy the practical activity and the explanation is best given after they have results they can talk about. If they work in groups using different inks to write questions they can pass those messages to another group who can develop the message and send the answer to the question back. A good way of recording this work is to get the pupils to write a story involving the ink they have used for their experiment.

Curriculum range:

All ages can take part in this activity but at different levels since the aim is to gain some understanding of the thinking of the scientist and artist with regard to the properties of materials. It links with:

• setting up simple practical enquiries, comparative and fair tests;
• reporting on findings from enquiries and observations, including oral and written explanations, displays or presentations of results and conclusions;
• using straightforward scientific evidence to answer questions or to support their findings;
• comparing and grouping together everyday materials on the basis of their properties such as solubility and transparency;
• knowing that some materials will react to produce a visible product;
• building a more systematic understanding of those types of materials by exploring and comparing the properties of a broad range of materials;
• asking questions and develop a line of enquiry based on observations of the real world, alongside prior knowledge and experience;
• using appropriate techniques, apparatus, and materials during laboratory work, paying attention to health and safety;
• making and recording observations and evaluate the reliability of methods and suggest possible improvements;
• presenting observations using appropriate methods;
• interpret observations, identifying patterns to draw conclusions;
• presenting reasoned explanations, including explaining data in relation to predictions and hypotheses;
• the concept of a chemical change, oxidation, pH and decomposition; and
• knowing about the idea of a chemical change, mixture and solution, including dissolving.

Hazard warnings:

Students should wear eye protection and disposable gloves.

Supervision may be necessary when the students are using the heating equipment.

Ammonia is TOXIC 

Concentrated ammonia is CORROSIVE & DANGEROUS FOR THE ENVIRONMENT

Suggest not using. Ammonia gas is TOXIC. Ammonia concentrate is CORROSIVE & DANGEROUS FOR THE ENVIRONMENT. This would need a very well ventilated room and student behaviour assessment also CLEAPSS advises a maximum of 2M for Year 7.

Sodium carbonate (solid) is IRRITANT

Phenolphthalein is HIGHLY FLAMMABLE & HARMFUL

Thymolphthalein is HIGHLY FLAMMABLE & HARMFUL

Copper (II) sulphate (solid) is HARMFUL & DANGEROUS FOR THE ENVIRONMENT

Lead (II) nitrate is TOXIC & DANGEROUS FOR THE ENVIRONMENT.

Iron sulphate (solid) is HARMFUL 

Sodium sulphide is CORROSIVE & DANGEROUS FOR THE ENVIRONMENT

Cobalt chloride is TOXIC & DANGEROUS FOR THE ENVIRONMENT

Iodine is HARMFUL (will stain skin but is low hazard at 0.1M)

Iodine solution should not be present with Ammonia solution. An explosive mixture can be formed.

Potassium ferricyanide should not be present with Ammonia because an explosive mixture can be formed. It should also not be present where concentrated acid could be added because it would produce TOXIC gases.

Potassium ferricyanide & phenolphthalein should not be used where there are naked flames (do not use Bunsen burners).

Some of the metal compounds such as copper, cobalt, and lead can be toxic in varying quantities and can be an irritant if the liquid is spilt or put on the skin.

Ultra-violet light can be harmful to eyes so pupils should be supervised when handling the lamp or they can observe as an adult uses the lamp. Portable counterfeit money detectors can be used for this and are easily sourced and reasonably priced.

Use one of the methods below to write a question on a piece of white paper. Pass the message to another group who will develop your message and then write an answer to the question and pass it back to you to develop. It would be good to use different types of ink as advised by your teacher.

Heat-Activated Invisible Inks:

These inks are best for younger children since most of the chemicals are household and generally less hazardous. They can be developed by heat generally ironing them with a hot iron or placing them in an oven or (on a white tile) on a hotplate.

Any of the following:

• Any acidic fruit juice (e.g. lemon, apple or orange juice) 
• Baking soda (sodium bicarbonate) solution or 1 M sodium hydrogen carbonate
• Vinegar or 1 M ethanoic acid
• Soapy water or 0.1 M sodium carbonate hydrated
• Sucrose (table sugar) solution (1 tsp in 10 cm 3 water)
• White tiles (For using on the hotplate. The tiles heat up but protect the paper from burning)

Inks Developed by Chemical Reactions:

These are best used with secondary students and most could be used comfortably with lower secondary students. Many of them work as pH indicators, so paint or spray a suspected message with a base (eg sodium carbonate solution) or an acid (e.g. lemon juice). Some of these inks will also reveal their message when heated (e.g. vinegar). The substances in milk weaken the paper and may be more susceptible to heat than the paper, so although the message dries clear, the paper weakens and darkens where the milk was applied.

• Phenolphthalein (pH indicator) HIGHLY FLAMMABLE & HARMFUL, developed by sodium carbonate (Solid is IRRITANT – solution is LOW HAZARD) (or another base). Suggest not using. Ammonia gas is TOXIC. Ammonia concentrate is CORROSIVE & DANGEROUS FOR THE ENVIRONMENT. This would need a very well ventilated room and student behaviour assessment also CLEAPSS advises a maximum of 2M for Year 7.
• thymolphthalein HIGHLY FLAMMABLE & HARMFUL, developed by sodium carbonate (Solid is IRRITANT – solution is LOW HAZARD) (or another base) 
• vinegar or 1 M (ethanoic) acetic acid, developed by red cabbage water 
• ammonia (1 M ammonium hydroxide) , developed by red cabbage water 
• 1 M sodium hydrogen carbonate, sodium bicarbonate (baking soda), developed by grape juice 
• 1 M sodium chloride (table salt), developed by 0.1 M silver nitrate 
• 1 M copper sulfate, developed by sodium iodide, sodium carbonate, or 1 M ammonium hydroxide 
• 0.005 M lead (II) nitrate, developed by 1 M sodium iodide (Lead (II) nitrate is TOXIC at = > 0.01M and HARMFUL in solutions less than this.)
• 1 M iron sulfate IRRITANT, developed by 0.1 M sodium carbonate
• 1% starch solution (e.g. corn starch or potato starch), developed by 0.1 M iodine solution 
• Lemon juice, developed by 0.1 M iodine solution
• Paintbrushes (and/or straws, cotton buds) 

Inks Developed by Ultraviolet Light (Black Light):

These can be used with younger children but the chemistry is more complex so the theory is best left to secondary age students. Most of the inks that become visible when you shine an ultra violet light on them also would become visible if you heat the paper.

• Dilute laundry detergent (the bluing agent glows) or 1 M sodium carbonate hydrated (Lead (II) nitrate is TOXIC at => 0.0 M and HARMFUL in solutions less than this.)
• tonic water (quinine glows) 
• vitamin B-12 dissolved in vinegar 

Technical notes:

Because of the wide range of materials, teachers should select either a few of the materials or group students to allow a wider range of materials to be investigated. If using groups then sufficient time needs to be allowed for whole class reporting on the results and evaluation of the materials being used.

Provide solutions of solids if preferred. Solutions made of one spatula measure or teaspoon mixed with 10 cm3 of water is sufficient.

The discussion can be approached using the Special Operatives Executive (SOE) properties for ‘ideal’ invisible ink as the evaluation criteria. The invisible ink could be dried with a hairdryer or on a warm radiator initially.

The hotplate can be used on a low heat without the white tile, but it will have to be supervised as the paper could burn. It is safer to use a white tile on the hotplate to place the paper onto. It takes about 20–30 seconds on average on a low to medium heat setting for the message to appear. This means that a class practical could be carried out using a hotplate without congestion.

The oven method takes longer and there is less control over when to discontinue heating.

There is more control over the chemicals if paintbrushes, etc. are used instead of spray bottles.

After writing, the message should not be visible either by inclining the paper and using oblique incident light or seeing any residue on the surface of the paper.

When developed the message should be visible and readable so students should be able to inform others of the message. The message is given to another group who develops the message and reports to the group on what the message said.

Good results can be obtained from the heat method on milk, sodium hydrogen carbonate solution, vinegar (ethanoic acid), sugar solution and soapy water (sodium carbonate solution). 

The following work well from the chemical reaction method, copper sulphate and ammonium hydroxide, copper sulphate and sodium carbonate, phenolphthalein and sodium carbonate.

Invisible ink: student sheet

Invisible ink: teacher sheet, additional information.

Acknowledgement to Royal Society of Chemistry:

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Wonder of the Day #1185

How Does Invisible Ink Work?

TECHNOLOGY — Inventions

Have You Ever Wondered...

• How does invisible ink work?
• What common household substances can be used to make invisible ink?
• What things can you do to reveal a message written in invisible ink?
• abnormalities ,
• abnormality ,
• activated ,
• admission ,
• amusement ,
• brightener ,
• chemically ,
• colorless ,
• detergent ,
• developer ,
• household ,
• invisible ,
• knowledge ,
• substance ,
• ultraviolet ,
• Abnormalities ,
• Abnormality ,
• Activated ,
• Admission ,
• Amusement ,
• Brightener ,
• Chemically ,
• Colorless ,
• Detergent ,
• Developer ,
• Household ,
• Invisible ,
• Knowledge ,
• Substance ,
• Ultraviolet ,

Today’s Wonder of the Day was inspired by Julia. Julia Wonders , “ How do invisible ink pens work? ” Thanks for WONDERing with us, Julia!

ATTENTION, SECRET WONDER AGENTS: Today's Wonder, should you choose to explore it, is one of great mystery…and science. Your challenge is to leave a written message on a piece of paper in a way that people won't see the message , even if they stare right at it.

What do you think? How would you answer the challenge? It can be fun to think like a spy and figure out ways to send secret messages . One way to do this (and answer the challenge) is to use invisible ink .

One very simple form of invisible ink is heat activated. These inks can be made from many types of organic liquid . Once the message dries on the paper, it is invisible .

When the ink is exposed to heat , such as under an iron or over a candle flame or 100-watt light bulb, the acids in the liquid turn a different color and the message becomes visible. You can find many heat -activated invisible inks right inside your kitchen, including clear soda, lemon juice, apple juice, onion juice, milk, soapy water, sugar water, and vinegar.

Another type of invisible ink is chemically activated. Chemically-activated inks can be made from any two chemical substances that are colorless until mixed with one another. When the message receiver adds the second chemical developer, the chemical reaction between both substances causes the color to change and the message to appear. Vinegar alone can be heat -activated, but if you add red cabbage water instead of heat , it becomes a chemically-activated invisible ink .

A third kind of invisible ink is a favorite of amusement parks. Long ago, if you needed to leave an amusement park to go to your car, they would simply stamp your hand. When you returned to the park gate, as long as you had the stamp , you didn't have to pay to come back inside. These ink stamps were easy to copy and allowed people to sneak in without ever paying for a ticket.

Today, many amusement parks use light -activated invisible inks. If you need to leave the park, they will stamp your hand, but you may be surprised when you look down to find nothing is there. When you return to the park, they will ask you to put your hand under a special light , and just like magic, a glowing stamp imprint appears.

Light -activated inks work because they contain substances that glow under different types of light , but remain invisible to the naked eye. This means no big, ugly stamp marks on your hand and no more free admission for anyone trying to sneak in. Examples of light -activated invisible inks include laundry detergents containing brighteners , soaps, and human saliva .

Invisible ink may not be obvious to the naked eye, but pen scratches and abnormalities on the paper can be telltale signs of its presence. Some inks are easier to develop than others, which means anyone with knowledge of invisible inks may be able to decode your message .

For example, let's imagine you use soapy water to write your message . If someone found your paper, they might use heat , chemicals and ultraviolet light . Since soapy water is reactive to each of these, it wouldn't take them long to reveal your top-secret message .

Wonder What's Next?

Tomorrow’s Wonder of the Day is full of hot air. Hope you’re not afraid of heights!

Are you ready to fine tune your spycraft? Recruit a couple of super-sneaky friends or family members to help you explore one or more of the following secret activities:

To create a hidden message, just dip a toothpick in your chosen ingredient and write your message. Once the paper has dried, ask an adult for help applying a warm iron to the paper. As the paper heats up, your message will magically reappear. Which invisible ink is your favorite?

• If you were a spy today, would you trust invisible inks to send secret messages? Why or why not? What other means of communication might you use instead to communicate secretly with other spies or government agents? What are the pros and cons of these other methods? Is there any completely safe and secure means of communicating in the Internet age?
• Making your message invisible is one way to try to hide it. But did you know that it's also possible to hide it in plain sight? What are we talking about? Secret codes, of course! Jump online to check out these 3 Secret Codes you can learn to use at home. Instead of writing your message with invisible ink, write it in regular ink in a secret code. Teach the code to a friend or family member, so that they can decode it. Ask them to encode a super-secret message for you to decode, too!
• Soapy water
• Sugar water
• Lemon juice

Did you get it?

Wonder contributors.

We’d like to thank:

Amelya , Amelya and Veronica for contributing questions about today’s Wonder topic!

Keep WONDERing with us!

Wonder Words

• ultraviolet

Hi Bailey! 

We're glad you found this Wonder helpful. Remember to cite your sources! Wonderopolis is the author and you can use the date accessed since we don't track publication/review dates. 

You're welcome, Fatima! Was there anything you were surprised about when reading this Wonder?

Sumanlata Prajapati

That's a great question, Wat! We hope you'll continue your Wonder Journey by researching your question online or at your local library! :)

Hi, Elizabeth! We're glad you're exploring the Wonder Words. In this Wonder the word is referring to a written message or note. We encourage you to continue to learn about the word. Maybe talk with your friends and family, too! :)

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Bryan Alvarado

That is a WONDERful Question, Bryan! We're not sure exactly why heat makes the message visible. However, we know it has to do with the chemical properties of the invisible ink. It seems to be reacting to the heat. Thanks for making us Wonder today, Bryan! :-)

We'll give you a hint, Ben. Try highlighting the space where the first paragraph should be. ;-)

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Ms. Davidson's Science C

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Question 1 of 3

The simplest invisible inks made from household substances, such as soapy water, are activated by what?

• a heat Correct!
• b atomic particles Not Quite!
• c flour Not Quite!
• d sound Not Quite!

Question 2 of 3

Today, many amusement parks use invisible inks for hand stamps that are activated by what?

• a heat Not Quite!
• b sweat Not Quite!
• c money Not Quite!
• d light Correct!

Question 3 of 3

Chemically-activated invisible inks can be made from any two chemicals that are what until mixed with each other?

• a odorless Not Quite!
• b colorless Correct!
• c orange Not Quite!
• d inedible Not Quite!

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Invisible Magic: Make your own secret messages and drawings!

Imagine being in an intense situation where you need to strategize with your team that is far away, but have no cell phones, email, or internet to talk to them. That’s the intense situation many found themselves in during war hundreds of years ago, who relied on invisible ink to secretly share war tactics and information.

In today’s experiment, we will be creating our own invisible ink.

Creating invisible ink can be done without extreme heat! Turmeric, nature’s pH indicator, changes the invisible baking soda (a base) ink to a very bright color, exposing your secret message.

So put your spy glasses on and create your own secret message!

How to make the Invisible Magic science experiment

Supplies you will need.

For this experiment, you will need the following:

• Water (1/4 cup)

Before you start

Turmeric can easily stain surfaces (and little hands), so place down a towel that you don’t mind getting yellow!

Instructions

Here is how to do this experiment with your child:

Step 1: Mix baking soda and water

In a small dish, mix 1/4 cup of baking soda with 1/4 cup of water.

The baking soda will settle to the bottom of the bowl, but you can just dip the Q-tip (in the next step) into the solution to pick up some baking soda.

Step 2: Write your message

Dip your Q-tip or small paintbrush into the baking soda mixture and write your message on a piece of paper.

It can be words or even some fun art. Get creative!

Allow this to dry for about 10-15 minutes.

Step 3: Mix turmeric and alcohol to reveal message

Mix 1/4 cup of alcohol with turmeric. The consistency should be close to a very runny paste.

Using your small paintbrush, brush the turmeric mixture over the paper to reveal the message.

The science behind the Invisible Magic experiment

This experiment teaches:

The history of invisible ink

• How invisible ink is used today

How it works

The invisible ink experiment works by first writing a message on a piece of paper using a baking soda and water mixture. The message dries and it appears that there is nothing written on the piece of paper.

Using the turmeric and alcohol mixture, we paint over the message to reveal what was written in baking soda.

Since turmeric is a natural pH indicator and baking soda has a higher pH level, it makes the message appear in a different color than the yellow “paint” of the turmeric.

The first record of invisible ink came from Pliny the Elder over 2,000 years ago. He used milk of the tithymalus plant as the “ink” and sprinkled ashes on the dried ink to expose the message.

Since then, there have been several different concoctions that produce these encripted messages, including ferrous sulfate and water during the Revolutionary War. These secret messages were used to secretly communicate war tactics, including between spies!

If you have ever tried to test your pool water to see how much chlorine or salt you should put in? If so, you were checking the pH levels of your pool to ensure it’s balanaced properly!

In our case, the spice turmeric is actually a natural pH indicator.

When we paint the turmeric and alcohol mixture over the dried baking soda message, the turmeric exposes the pH level of the baking soda with a deep red color.

What are some other real-life examples of how pH is tested?

• Food (to check for bacteria growth)
• Beverages (to check for acidity)
• Wastewater treatment
• When pH of our mouths reduces, it means our teeth are decaying
• The acidity of plant fertilizers

How is invisible ink used today?

There are other types of invisible ink out there, ones that do not necessarily require a turmeric mixture to reveal something.

For example, there is an invisible ink used today that requires UV light to expose a message or picture. That type of invisible ink is used for tickets for readmission to an event, lottery tickets, or to mark items in case of theft.

More creative experiments that have fun with drawing to try out with your child

• Scribble Bot: A cute robot that draws!
• Swinging Art Salt Pendulum: Create beautiful art while talking about physics

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This experiment is a really fun one, and there are so many ways to change it up! Scribble Bots utilizes a small motor to draw on a large piece of paper with markers. It's a fun lesson on robotics...

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• Why We’re Unique

A Secret Letter with Invisible Ink

Introduction: (initial observation).

Developing recipes for invisible ink is the task of scientists. Putting it to use is generally the work of spies and others in pursuit of nefarious deeds. It’s the work of the sleuth to figure it all out, at least that’s the way most good mystery novels work! But invisible ink has also had its place in history.

Artifacts from World War II turn up quite frequently, but a   certain postcard turned up a few years ago which caught everyone’s interest. The postcard had been sent out of Poland during the occupation. There wasn’t anything of interest to the Germans on the postcard, or so they thought.

Beneath a one sentence letter on the postcard was a message written in invisible ink! The message makes an urgent request for supplies, including invisible ink. Fragmented sentences read like a nightmare, describing a Nazi death camp with gas chambers. It told a story about a person we might not have even known about otherwise. Invisible ink had made this possible, but what is invisible ink? And how does it work?

Dear This project guide contains information that you need in order to start your project. If you have any questions or need more support about this project, click on the “ Ask Question ” button on the top of this page to send me a message.

If you are new in doing science project, click on “ How to Start ” in the main page. There you will find helpful links that describe different types of science projects, scientific method, variables, hypothesis, graph, abstract and all other general basics that you need to know.

Project advisor

Adult help and supervision is required.

Information gathering:.

Find out invisible inks. Read books, magazines or ask professionals who might know in order to learn about the methods of making invisible ink and revealing them. Keep track of where you got your information from. Following are some related links:

http://detnews.com/2001/nation/0106/09/nation-234164.htm

Spy letters of the American revolution

HOLOCAUST Tales of Myth

Question/ Purpose:

What do you want to find out? Write a statement that describes what you want to do. Use your observations and questions to write the statement.

What are some ways to write secret messages? What material can be used as invisible ink?

Identify Variables:

When you think you know what variables may be involved, think about ways to change one at a time. If you change more than one at a time, you will not know what variable is causing your observation. Sometimes variables are linked and work together to cause something. At first, try to choose variables that you think act independently of each other.

Independent variable in this project is the type of liquid that we may use as invisible ink. The dependent variables are the visibility of ink before and after the revealing process.

Hypothesis:

Based on your gathered information, make an educated guess about what types of things affect the system you are working with. Identifying variables is necessary before you can make a hypothesis.

My hypothesis is that onion and potato can be used as invisible inks. This hypothesis is based on my observation of roasting and frying onion and potato that makes them to change color and burn as soon as they lose their water. While performing experiments I will also test other material such as vinegar, lemon juice and milk to see if they can be used as invisible ink.

Experiment Design:

Design an experiment to test each hypothesis. Make a step-by-step list of what you will do to answer each question. This list is called an experimental procedure. For an experiment to give answers you can trust, it must have a “control.” A control is an additional experimental trial or run. It is a separate experiment, done exactly like the others. The only difference is that no experimental variables are changed. A control is a neutral “reference point” for comparison that allows you to see what changing a variable does by comparing it to not changing anything. Dependable controls are sometimes very hard to develop. They can be the hardest part of a project. Without a control you cannot be sure that changing the variable causes your observations. A series of experiments that includes a control is called a “controlled experiment.”

Experiment 1:

In this experiment we will see if lemon onion juice can be used as in invisible ink. We will try to write secret messages with different possible invisible inks, and try revealing the secrets using a heat source.

Use any juice making method that is easier for you to make some onion juice. If your juice is not clear, use a coffee filter to filter any onion pieces and make clear juice.

Find something to write with such as a small brush, an old but clean fountain pen, or even just a Q-Tip or tooth pick. Providing that the paper is white, and providing you use your “ink” sparingly, the message is pretty much invisible to the eye. Be sparing in your use, though. Too much “ink” will cause the paper to buckle up a bit and the writing will show. And be sure that your writing implement is very clean and doesn’t leave traces of some old ink or paint.

Let the paper dry for about 10 minutes.

Use a hot plate, a burner or stove and carefully heat it up. Obviously, don’t let the paper catch fire…. (Pretty soon the message will turn up as brown writing.) .

Repeat this experiment with other possible liquids that may be used as invisible ink. vinegar, lemon juice and milk are among the liquids that will work. Potato juice did not work as good, try it yourself.

Note: You may also use an iron to reveal a secret message.

How it works is really quite simple. There are chemical compounds in the onion and lemon juice that have a low burning point. These are carbon compounds such as those that make caramel. When you hold the paper over heat, these compounds scorch and turn brown before the paper does, so they leave their mark and reveal the writing.

Experiment 2:

In this experiment we use starch solution as invisible ink. Then we use a chemical reaction between starch and iodine solution to reveal the message.

Materials Needed:

• Corn Starch
• Toothpicks or Cotton Swab
• Iodine Solution
• diluted iodine solution
• Small Sponge
• Mix a small amount of water with cornstarch in the pan and stir until smooth. (You may try one tea spoon starch with one cup of water)
• Heat the mixture for several minutes. Stir.
• Dip a toothpick into the cornstarch and water mixture and write with the mixture on paper. Let the paper dry.
• To observe the message, dip the small sponge into the iodine solution and carefully wipe the paper. Do not get the paper too wet. The message should appear purple.

Note: Many papers specially those used as copy paper or laser printer paper contain starch, so they can not be used for this experiment. In order to find out which paper does not have starch at all, use a drop of iodine solution. If the paper does not turn blue, it does not have starch.

Experiment 3:

In this experiment we use another chemical reaction to reveal a secret message

• phenolphthalein (available from MiniScience.com and ChemicalStore.com)
• Rubbing Alcohol
• Paper Toweling – higher quality ones work better
• Windex™ – with ammonia D
• Use the rubbing alcohol to dissolve the phenolphthalein. If you a solution of phenolphthalein you will not have to do this.
• Use a paintbrush to paint your message on the paper towel.
• After it dries you can see nothing until you spray the Windex on the area. Then the words you painted will appear as pink letters.

Why does it work?

Phenolphthalein was first synthesized in 1880 and has long been known to change color depending on whether it is in acidic or basic conditions. It is colorless under acidic (or neutral) conditions and pink/red in basic solutions. The Windex™ contains a chemical, ammonia, that turns the conditions basic. By spraying the ammonia on the paper, the phenolphthalein turns pink and you can see the letters that were painted in advance.

Do I need to use phenolphthalein?

Old ExLax™ tablets contained phenolphthalein. You may find some old instructions for this experiment suggesting the use of ExLax instead of phenolphthalein. Please note that new ExLax tablets do not contain phenolphthalein.

Experiment 4:

In this experiment we compare different invisible inks to see which one will reveal faster. We will then enter our results in a data table and use it to make a bar graph.

Adult supervision and support is needed for this experiment.

• Lemon or lime juice
• Onion Juice
• Toothpicks or Cotton Swab for writing
• Heat source (Hair dryer or toaster oven)
• Timer or clock

• Get a sheet of copy paper and cut it in 4 identical pieces.
• In the middle of each paper draw a 3 cell table (shown above)
• Use a toothpick and milk to write the word MILK in the upper cell.
• Use a toothpick and onion juice to write the word ONION in the middle cell.
• Use a toothpick and Lemon juice to write the word Lemon Juice in the lower cell.
• Repeat the steps 3 to 5 with all four pieces of paper and allow at least one hour for the papers to dry.
• Heat up one of the papers with a hair dryer or toaster oven and record the time it takes for each of the invisible inks to reveal. Record that time in your data table.
• Repeat the heating process with the remaining 3 papers (one at a time) and record the results.

To calculate the average time to reveal for each ink you must add the four values you recorded and then divide the total by 4.

Make a bar graph:

Draw 3 vertical bars and name them Milk, Onion and Lemon Juice. The height of each bar will represent the average time to reveal for that specific invisible ink. Write the average reveal time above each bar. Name your graph “Relative Reveal Time for household invisible inks”.

Example: If the average reveal time for onion is 25 seconds, then the height of the bar may be 25 mm or 25 centimeters or any other unit you like.

Materials and Equipment:

• Onion juice, vinegar, lemon juice, milk
• toothpicks or paintbrushes
• pieces of paper
• a heat source

Results of Experiment (Observation):

Experiments are often done in series. A series of experiments can be done by changing one variable a different amount each time. A series of experiments is made up of separate experimental “runs.” During each run you make a measurement of how much the variable affected the system under study. For each run, a different amount of change in the variable is used. This produces a different amount of response in the system. You measure this response, or record data, in a table for this purpose. This is considered “raw data” since it has not been processed or interpreted yet. When raw data gets processed mathematically, for example, it becomes results.

Calculations:

No calculation is required.

Summary of Results:

Summarize what happened. This can be in the form of a table of processed numerical data, or graphs. It could also be a written statement of what occurred during experiments.

It is from calculations using recorded data that tables and graphs are made. Studying tables and graphs, we can see trends that tell us how different variables cause our observations. Based on these trends, we can draw conclusions about the system under study. These conclusions help us confirm or deny our original hypothesis. Often, mathematical equations can be made from graphs. These equations allow us to predict how a change will affect the system without the need to do additional experiments. Advanced levels of experimental science rely heavily on graphical and mathematical analysis of data. At this level, science becomes even more interesting and powerful.

Conclusion:

Using the trends in your experimental data and your experimental observations, try to answer your original questions. Is your hypothesis correct? Now is the time to pull together what happened, and assess the experiments you did.

At least 5 different kinds of the invisible ink can be made, using white wine, vinegar, lemon juice, apple juice, milk, iced tea, and orange juice. And if you have time, see if other types of acidic fruit juices also work.

Related Questions & Answers:

What you have learned may allow you to answer other questions. Many questions are related. Several new questions may have occurred to you while doing experiments. You may now be able to understand or verify things that you discovered when gathering information for the project. Questions lead to more questions, which lead to additional hypothesis that need to be tested.

Possible Errors:

If you did not observe anything different than what happened with your control, the variable you changed may not affect the system you are investigating. If you did not observe a consistent, reproducible trend in your series of experimental runs there may be experimental errors affecting your results. The first thing to check is how you are making your measurements. Is the measurement method questionable or unreliable? Maybe you are reading a scale incorrectly, or maybe the measuring instrument is working erratically.

If you determine that experimental errors are influencing your results, carefully rethink the design of your experiments. Review each step of the procedure to find sources of potential errors. If possible, have a scientist review the procedure with you. Sometimes the designer of an experiment can miss the obvious.

References:

List of References

It is always important for students, parents and teachers to know a good source for science related equipment and supplies they need for their science activities. Please note that many online stores for science supplies are managed by MiniScience.

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Invisible ink.

Science at Home for Kids

Easy and fun science experiments using household items! Follow us on Instagram @scienceathomekids for more cool science!

Invisible Ink

Do you want to write cool, invisible messages to your friends and family members? Well, this is easier than you might think! All you need to do is gather a few items from around the house and you can make your own invisible ink!

What you need:

• Baking soda
• Cranberry or grape juice
• Cotton swab
• White paper

• Mix equal parts of baking soda and water together (I used 1 tablespoon of each).

• Use your cotton swab to write a secret message on your paper.

• Allow the message to dry.
• Use your paintbrush to brush the cranberry or grape juice over your secret message.

• Watch the message magically appear!

What makes the message appear?

Baking soda has a pH of 8, which means it is a base. Since baking soda is white, when we write with the baking soda and water mixture on the paper, it blends in with the paper and does not appear. Cranberry juice has a pH of about 2.5, which makes it an acid. The cranberry juice also has a specific molecule in it that acts as an acid-base indicator, which means it can change colors depending on the amount of acid or base present. When the cranberry juice is brushed onto the basic message, the message turns a different color than the paper due to their differences in pH.

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Invisible Ink Experiment (With Lemon Juice & Salt Solution)

• April 16, 2021
• 10 Minute Science , 5-6 Year Olds , Chemistry , Household Items

Today we are going to show you – how make your very own invisible ink at home.

Yes, using invisible ink, we can write and leave secret messages like secret agents do!

It is really easy to do and really fun to play with.

Materials Required to Make Invisible Ink

You just need to keep the below list of items handy on your work table.

• Paint Brush or Earbuds

That’s it! If you have the above supplies, then you are good to go to explore this activity.

Directions to Prepare Invisible Ink

We are going to make homemade invisible ink in two different methods using two different key ingredients.

Method-1: Lemon Juice Invisible Ink Experiment

Step-1:  Take fresh and ripen lemons and squeeze out the juice using your fingers or any squeezing machine into a small bowl.

Step-2:  Now, add a little amount of water into the bowl containing lemon juice. Just 10-15 drops of water are enough. Then, mix or stir the mixture of lemon juice and water using a fresh spoon. That’s it. Our invisible ink is ready to make magical tricks on paper.

Step-3:  As step-3, Pick a plain white paper and keep it ready on your table for writing a secret message of yours. Then, take a paintbrush and dip it in the bowl containing the lemon juice and water mixture. Here you can also use a cotton swab or earbud to write on the paper.

Step-4:  Using the immersed paintbrush, write some text or message of your choice on the paper and let it dry. Once the liquid dried, you cannot see your text completely. So, that is the reason we need to dry the paper properly.

Step-5:  As a final step, bring the paper over a heat source, i.e., a candle or lighter or light bulb. And wait for some time until you see the text on the paper appear.

Note:  You need to make sure the paper is close to the heat source but not too close to avoid catching fire.

Method-2: Preparing Invisible Ink Using Salt

Step-1:  Pick a small bowl and add a certain amount of salt. Then, pour some amount of water into it until the salt dissolves completely in the water. You can use this salt solution as invisible ink.

Step-2:  After you make saltwater in the right proportions, which is our invisible ink, we continue performing the activity same as method-1 from step-3 to step-5.

Step-3:  Check the results and observe whether you get the same result as method-1.

Suggested: Explore wonderful science experiments with Salt

Science Behind Invisible Ink

Lemon juice is a great source of carbon compounds. Since it is an organic substance, it also exhibits oxidizing properties.

These carbon compounds in lemon juice are colorless at room temperature.

However, when they are exposed to heat – these carbon compounds breaks down and release the carbon.

When carbon comes in contact with oxygen present in the air – oxidation occurs. It converts the substance to light or dark brown in color. Prolonged oxidation may even create black color signifying more carbons.

That is the reason your writings on the paper using lemon juice and water mixture turn out into brown color when exposed to the candle.

To make the text written on the paper invisible, we are making the concentrated lemon juice very light by mixing a few water drops.

Diluted lemon juice on the paper gets dry and completely disappears, giving the impression that nothing is written on the paper.

But when you expose to heat or light source, the lemon juice gets oxidized and appears as brown color text. Oxidation is the process of combining carbon atoms with the air and turning light things into dark brown.

Extension Ideas

• Try creating invisible ink using other substances such as milk, honey, wine, orange juice and onion juice.
• Besides, you can also use other chemical substances that would glow in black light.

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Science Fun

Easy Invisible Ink Cool Science Experiment

In this cool science experiment, we’re going to make easy invisible ink. Creating invisible ink is a lot of fun and you can even pretend to be a secret undercover agent and keep all of your secret codes and messages concealed from other people. You simply need some general household items to create and enjoy easy invisible ink. 

• Lamp or flashlight
• Blank white paper
• Cotton ball
• A lemon or a bottle of real lemon juice

Instructions:

• Squish and squeeze some lemon juice into the bowl and include a few drops of water.
• Stir the water and lemon juice using the spoon.
• Dip the cotton ball into your solution and then use the cotton ball to create a secret message on the blank white paper.
• Allow the lemon juice and water solution to dry completely.
• When your ready to reveal your secret message, warm up the paper by positioning it near a light bulb or holding the beam from a flashlight onto the area where the secret message was written.
• Observe what happens. 

EXPLORE AWESOME SCIENCE EXPERIMENT VIDEOS!

How it Works:

Lemon juice contains carbon compounds which are invisible at room temperature. The heat from the light source breaks down the compounds and releases the carbon. Once the carbon interacts with air, it oxidizes and turns brown, revealing your secret message. 

Make This A Science Project:

Try different types of citrus fruits and fruit juices. Try different types and colors of paper. Try UV light. Try vinegar. 

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Invisible Ink: Secret Messages and Spy Science Explored

Table of Contents

Invisible ink has fascinated both history buffs and science enthusiasts alike. It’s a unique intersection where chemistry meets clandestine communication, playing a critical role throughout espionage history. Secret messages written with invisible ink require specific methods for their creation and revelation, often relying on everyday materials. From lemon juice to more sophisticated chemicals, these hidden communications have shaped the craft of spies and influenced both ancient and modern warfare.

The science behind invisible inks is both intriguing and accessible, making it a popular topic for educational experiments and hobbyists. While the historical use of invisible inks dates back to ancient times, modern advancements have improved their effectiveness and the ability to keep messages concealed. Today, invisible ink has found its place in both playful activities and serious applications, giving it a diverse and interesting place in the world of secret messaging and spy science.

Michelle Connolly, a seasoned educational consultant with 16 years of classroom experience, points out, “The allure of invisible ink lies in its dual appeal to our love for mystery and the beauty of science.” This blend of intrigue and educational value makes invisible inks an excellent topic for engaging young minds in the principles of chemistry and the excitement of discovery.

Key Takeaways

• Invisible ink is at the crossroads of historical espionage and chemical science.
• Secret messages can be crafted with common household items and specialised substances.
• Modern uses of invisible ink range from educational experiments to security measures.

The Science of Invisible Inks

Invisible ink, also known as ‘secret ink’, is not just a tool of spy novels, but a real application of chemistry that has been used throughout history to send hidden messages.

Chemical Properties

Invisible inks are substances that you can apply onto a surface, such as paper, to write messages that are invisible to the naked eye under normal light. To read the concealed writing, you often need a specific chemical reaction or a change in physical conditions, like exposure to heat or ultraviolet light. Chemists have designed a multitude of invisible inks, with each type having unique chemical properties that dictate how the messages can be revealed.

For instance, certain invisible inks are based on organic substances that become visible under heat. These include lemon juice or milk, which when heated, are oxidised, causing a colour change which makes the secret writing appear. Other inks may rely on more complex chemical reactions where the message only becomes visible under specific chemical conditions.

Acid-Base Reactions

Several invisible inks function based on acid-base reactions, employing the concept of pH indicators. An acid, such as citric acid from a lemon, can be neutralised by a base, or vice versa. To reveal the message penned with a pH-sensitive ink, you might either dust it with a powder that reacts to the acid or base or expose it to an acid or base vapour.

Invisible inks that respond to pH changes are much like the litmus tests used in chemistry labs. When the acidity of the inked paper is altered, the ink changes colour and the message is thus uncovered. For example, a message written with a diluted solution of baking soda (a mild base), can be revealed by swabbing the paper with grape juice, which acts as a pH indicator changing colour when it encounters the base.

Utilising these chemical properties and reactions, spies and secret agents have been able to convey hidden messages through what appears to be a blank piece of paper. Invisible inks require both careful preparation and heat , air , or specific chemical substances to expose the hidden messages. The application of heat, for example, can cause a chemical reaction to occur, leading to the oxidation of the invisible ink and revealing the message.

Remember, whether you’re a budding chemist or simply curious about the science behind hidden messages, understanding the reactions at play can turn an ordinary piece of paper into a secret missive, just waiting to be uncovered by the right chemical partner or physical change.

Historical Use of Invisible Inks

Invisible inks have played a crucial role in communication throughout history, offering a way to conceal messages from unintended recipients. These inks have been pivotal in shaping the outcomes of wars and in the development of espionage tactics.

Ancient Times

In ancient times, the use of invisible ink can be traced back to notable figures such as Ovid. He suggested messages could be written in milk, which would only be revealed when heated. During the Revolutionary War, George Washington utilised invisible ink to relay secret information, emphasising the importance of such techniques in times of conflict.

With the onset of World War I , invisible inks became a common tool for espionage. The Germans , among others, developed ways to use them to send covert communications. During World War II , MI6 in London refined invisible ink methods, which included inks that could only be read under ultraviolet light, advancing the science of secret messages significantly.

Military Intelligence

The United States further embraced invisible ink for military intelligence. Various substances like lemon juice, vinegar, and even bodily fluids were employed as invisible inks. Their usage was not only a craft of wartime spycraft but also a subject of continuous scientific investigation to create more sophisticated methods.

“Understanding history adds context to the present, and the narrative of invisible inks helps us appreciate the evolution of communication and secrecy,” reflects Michelle Connolly — educational consultant with a wealth of classroom experience.

Everyday Materials for Secret Writing

You can create secret messages using ingredients found right in your own kitchen. These common substances can be the key to crafting invisible ink and revealing messages with ease.

Common Acids and Bases

Acids such as lemon juice and vinegar are readily available and work well as invisible inks. Apply the juice or vinegar to paper using a cotton swab or a thin brush to write your message. The acidity in these liquids breaks down the paper slightly and becomes visible when you heat the paper. Michelle Connolly, a prominent educator with a wealth of experience, says “Simple kitchen supplies like lemon juice can unveil the curious world of secret messages to children, making science both accessible and engaging.”

Bases such as baking soda create a chemical reaction when tested with iodine or heated. Baking soda solutions can be used for writing invisible messages that later can be revealed by brushing over with a colored indicator.

Household Items

Your cupboard is a treasure trove of items for secret writing:

• Fruits : Citrus fruits like lemons provide natural acids that are perfect for making invisible ink.
• Starch : Creating a paste with starch and water can also yield a visible message when stained or heated.
• Apple Juice : Much like lemon juice, apple juice can oxidize and turn brown under heat, revealing hidden messages.
• Milk : A classic invisible ink, milk becomes visible when heated, as it browns more quickly than paper.

Utilise these household items to experiment with invisible ink:

• Fruits : Nature’s bounty in your home can teach you about the science of secret writing.
• Cupboard Staples : Look through your cupboards for everyday substances that can be your secret agents.

Remember, the science of secret messages doesn’t need complicated equipment; just a few items from around your house can unlock this fascinating world.

Creating and Revealing Invisible Messages

Invisible ink has been a pivotal tool in the art of secrecy, historically used to send concealed messages that could only be revealed through specific methods. Whether you’re a hobbyist dabbling in science experiments or an educator incorporating spy science into your curriculum, understanding the practical applications of these techniques can be both enlightening and engaging.

Writing Techniques

To create a message with invisible ink , one common household item you can use is lemon juice . Simply dip a cotton bud or a fine paintbrush in lemon juice and write your message on a piece of paper. Once the juice dries, your message will be invisible to the naked eye. This form of secret writing is not only simple but also a fascinating science experiment that can be included in an education al setting.

Another method involves using a heat source such as a lamp or candle. By carefully applying heat to the paper with the dried lemon juice, the message becomes visible due to the oxidising property of the juice. This shows a basic chemical reaction, which can be a practical way to introduce students to foundational science concepts.

Revealing Methods

After writing an invisible message, the key to seeing it lies in the revealing technique used. One such method is by applying heat . Gently heating the paper over a candle or holding it near a light bulb will make the message appear as the heat reacts with the chemicals in the invisible ink.

Alternatively, an iodine solution can reveal messages written with certain substances. By brushing the iodine solution over the paper, a chemical reaction occurs that causes the message to emerge.

For messages that require a more modern approach, ultraviolet light can be used. Invisible inks that react to UV light will appear clearly when exposed to such light sources, offering a more advanced and clandestine way to reveal encrypted communications.

Incorporating these methods of creating and revealing messages into a classroom can turn a simple science experiment into a magical and educational adventure . It’s a perfect way to spark interest in the practical application of scientific principles.

Michelle Connolly, the founder of LearningMole with over 16 years of classroom experience, says, “Invisible ink experiments are a splendid way to engage students with hands-on science. They’re not just learning about chemical reactions; they’re seeing them unfold right before their eyes.”

Advancements in Invisible Inking

In the realm of secret communications, invisible inking has undergone significant evolution. From chemically activated solutions to modern fluorescence techniques, the development of invisible ink has been critical for secure messaging.

Chemically-Activated Inks

Chemically-activated inks have a storied past in the espionage toolkit. These inks remain invisible until subjected to a specific chemical reaction. Silver nitrate , for instance, reacts under ultraviolet light to reveal the hidden message. Another common agent is phenolphthalein , which becomes visible when exposed to an alkaline substance. “It’s quite fascinating how a seemingly blank page can unveil secrets when brushed with the right substance,” remarks Michelle Connolly, an educational consultant with years of experience.

• Phenolphthalein : Visible under alkaline conditions
• Thymolphthalein : Appears blue with an alkaline solution
• Silver nitrate : Reacts to ultraviolet light

Disappearing Inks

Disappearing inks vanish after application, usually after a brief exposure to the air. This effect is often achieved with acids like lemon juice , which can be read by heating the paper. These inks have been used for centuries and continue to be a popular demonstration in educational settings to teach basic chemical reactions. Disappearing inks capture the essence of spy science, embodying the ‘now you see it, now you don’t’ phenomenon.

• Lemon juice
• Diluted cola

Fluorescent Techniques

Modern advancements have introduced fluorescent techniques, where the invisible message becomes visible under UV light . This method often employs inks made from substances found in laundry detergents and brighteners , which are invisible in natural light but glow under UV rays. Fluorescent paper can also be used, which is coated with materials that fluoresce when illuminated with UV light, providing a discrete and high-tech way to convey messages.

• Laundry detergents : Contain brighteners that fluoresce
• Fluorescent paper : Specially coated to glow under UV light

These strides in invisible inking technology have redefined the way we understand and utilise secrecy in communication. Whether through a simple acid-base reaction or sophisticated fluorescent compounds, the science of invisible ink continues to intrigue and inspire.

Practical Applications of Invisible Ink Today

Invisible ink still holds a place in modern society, from securing private information, fostering learning through play, to adding a layer of fun in various entertainment forms.

Privacy Concerns

In a world where privacy is increasingly treasured, invisible ink can provide an added layer of security for sensitive information. Whether it’s an individual safeguarding personal details or a company sending confidential messages, invisible messages created using secret formulations can help prevent unintended audiences from viewing private content.

Educational Purposes

For educational activities , various institutes, including LearningMole , utilise invisible ink to create engaging science experiments and secret writing challenges that fascinate students. According to Michelle Connolly, founder of LearningMole, “Weaving elements of mystery and secret codes into lessons not only captures children’s imagination but also enhances their understanding of chemical reactions.”

Entertainment

The entertainment sector frequently incorporates invisible ink into games and attractions to enchant participants. Escape rooms, treasure hunts, and board games often employ invisible messages as a playful means to unravel mysteries and discover hidden clues, enhancing the overall user experience.

By working these ancient techniques into contemporary applications, the art of invisible ink endures, transforming from traditional spy craft into a tool of trade for privacy, education, and entertainment alike.

Safety and Legality in the Use of Invisible Ink

When utilising invisible ink, understanding the corresponding safety protocols and legal implications is crucial. Ensuring the compounds used are non-toxic and that their application adheres to the law protects both the user and the public.

Legal Considerations

Invisible ink has a storied past in espionage, but its modern use is bound by various legal frameworks. While sending secret messages may seem innocuous, it is imperative to confirm that the content conforms to legal standards and is not associated with any illicit activities. In certain jurisdictions, the creation and transmission of hidden messages without proper authorisation can be considered a breach of law, especially if it involves sensitive or classified information.

Relevant Entities:

• Legal : Ensure compliance with local and international laws regarding the transmission of confidential information.
• Potassium Ferricyanide & Lead(ii) Nitrate : Be aware that some traditional inks made from these chemicals are regulated due to their toxic nature.

Safe Practices

When creating or using invisible inks, safety must be your top priority. It’s important to choose substances that are non-toxic and handle them with care. Many historical invisible inks contain hazardous materials and thus modern, safe alternatives should be sought.

Safety Tips:

• Ammonia & Potassium Ferricyanide : These compounds should be avoided as they can be harmful if inhaled or ingested.
• Lead(ii) Nitrate : This is a poisonous compound and should not be used in invisible ink due to the health risks involved.
• Poisonous Compounds : Substitute toxic substances with safer options like lemon juice or baking soda.

“Education is all about safe and accessible learning. With invisible ink, it’s the magic of chemistry that captivates and educates, but it must be practised safely,” says Michelle Connolly, founder of LearningMole, highlighting the importance of using non-toxic materials for educational science experiments.

Homemade Invisible Ink Recipes

Discover the fascinating world of espionage and secret communications with homemade invisible ink recipes. Whether you’re an amateur sleuth or just love science experiments, these simple concoctions can bring the magic of invisible messages to life right in your kitchen.

Natural Substances

Ingredients:

• Lemon Juice : Squeeze the juice of one lemon into a cup.
• Onion Juice : Crush a small onion to extract its juice.
• Vinegar : Use plain white vinegar for best results.

Instructions:

• Dip a cotton bud or fine paintbrush into your chosen natural substance.
• Write your message on a piece of paper.
• Let the message dry completely.
• To reveal the message, gently heat the paper using a light bulb or iron.

“Natural substances like lemon juice and onion juice are perfect for children to create their own invisible ink. It’s a safe, educational activity that combines science with a bit of mystery,” says Michelle Connolly, an educational consultant with extensive classroom experience.

Synthetic Solutions

• Baking Soda : Mix 1/4 teaspoon of baking soda with a couple of teaspoons of water in a cup.
• Alum and Vinegar : A teaspoon of alum mixed with a quarter cup of vinegar creates a more durable ink.
• Stir your selected synthetic solution until the solid is completely dissolved.
• Use a paintbrush or a dipped pen to inscribe your secret message onto paper.
• Allow the message to dry—this might be invisible or appear as a faint outline depending on the paper.
• To make the writing appear, paint over the paper with a mixture of 1 part iodine to 10 parts water.

Michelle Connolly comments, “Creating invisible ink with substances like baking soda is not just fun, it also introduces children to basic chemical reactions, fostering a love for science through hands-on experimentation.”

The Art of Decoy and Concealment

In the realm of clandestine communication , the use of decoys and concealment tactics plays a crucial role. It’s a dance of hidden messages and distractions designed to mislead whilst guarding the truth.

Ciphers and Codes

Ciphers and codes are the linchpins of hidden messages . They transform regular text into obscure symbols or letters, offering protection until they reach the intended recipient. You might encounter a message written in regular ink that appears innocuous yet contains a ciphered missive meant only for a specific reader. To reveal the secret , one must decode the message, an art form that requires both ingenuity and careful crafting .

Example: Imagine a letter discussing the weather. It might read, “Expect rain in cups of tea tomorrow.” To the untrained eye, it’s an everyday conversation. However, “cups of tea” could be a code indicating impending action.

Decoy Documents

Decoy documents serve to distract and deceive. They often coexist with genuine secret communications and are crafted to draw attention away from the sensitive information contained within a hidden message . The art form is to make the decoy compelling enough to divert attention.

Example: A decoy message might be a detailed schedule of an event meant to mislead. If discovered, it suggests a different location or time, while the true plans remain encoded within a message that seems mundane. The decoy must look authentic, often mimicking the attributes of a regular document but ultimately leading the reader astray.

“Effective secrecy is as much about the decoy as it is about the hidden message; one cannot exist without the other,” Michelle Connolly observes, reflecting on the interwoven nature of these tactics. Michelle, with 16 years of classroom experience, appreciates the depth of strategy involved in teaching the science of invisible ink and espionage.

Experimenting with Invisible Ink

Invisible ink isn’t just a staple of spy movies; it’s an engaging way to combine science with hands-on fun. You’ll discover how simple household items can be used to create and reveal secret messages.

Classroom Activities

In the realm of Education , experimenting with invisible ink can be both a fascinating Science Experiment and a creative classroom activity. To set up, you’ll need to gather a few materials:

• Red Cabbage Water : Acts as a natural pH indicator.
• Vinegar : An acidic substance that will react with your ‘ink’.
• Cotton Swab or Toothpick : Used to write messages.
• Bowl : To contain your experiment.

Here’s a simple activity:

• Blend red cabbage leaves with water to create your pH indicator.
• Dip a cotton swab into vinegar, and write a message on a piece of paper.
• Let the message dry completely, becoming invisible.
• Reveal the secret message by brushing the red cabbage water over the paper.

“Introducing children to science through something as engaging as invisible ink not only teaches them about chemical reactions but also stirs their imagination,” says Michelle Connolly, a pioneer in education with a wealth of classroom experience.

Fun Experiments

For a lighter take on the topic that’s perfect for a rainy afternoon, consider doing fun experiments with different substances as invisible inks. These are simple and safe activities that require materials such as:

• Baking soda solution

With these substances, the process is similar:

• Write with your chosen liquid using a cotton swab or toothpick.
• Allow the paper to dry.
• Hold the paper near a heat source, like a light bulb, and watch as the ink appears due to the heat reacting with the fibres and the ‘ink’.

Experiment with various ‘inks’ to see which ones reveal messages more clearly than others. Engage your curiosity and see if you can understand why some substances work better as invisible inks.

Frequently Asked Questions

In the intriguing world of espionage and secret communications, invisible ink has a rich history. These FAQs will shed light on how it works and how you can experiment with it yourself.

How can you create invisible ink without using heat?

You can create invisible ink using substances like lemon juice, milk, or vinegar. These acidic liquids react with the paper and become visible when they oxidise. Simply apply the liquid to paper, let it dry, and later reveal the message by holding the paper near a heat source.

Could you explain the science behind invisible ink experiments?

“Invisible ink experiments rely on chemical reactions. Certain inks become visible under specific conditions, such as heat or UV light, due to changes in pH or chemical structure,” explains Michelle Connolly, an educational consultant with over a decade and a half of classroom experience.

What could be a good hypothesis for a science project involving invisible ink?

A good hypothesis might be: If heat reveals invisible ink, then messages written with an acid-based ink can be read after being heated. You could test various substances to see how effectively they become visible.

How does baking soda work in making ink invisible?

Baking soda acts as a base and reacts with the cellulose in paper. When you heat the paper, the baking soda burns faster than the paper, revealing the message without catching fire.

What methods are effective in revealing messages written with invisible ink?

Several methods are effective, such as heat, UV light, and iodine fumes. Heat is commonly used to reveal messages written with acidic substances , while UV light can reveal inks that fluoresce. Iodine reacts with starch, such as in potato juice ink, turning it a dark colour.

Can you describe a simple experiment using lemon juice as invisible ink?

Certainly! Simply dip a cotton bud into lemon juice and write your message on a piece of paper. Let it dry completely. To reveal the message, gently warm the paper by holding it close to a light bulb (an adult should supervise this). The heat will cause the lemon juice to oxidise and turn brown, making your message appear. Michelle Connolly comments, “It’s a perfect blend of science and fun that captivates children’s imagination.”

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Invisible ink: Chemistry, Properties, and 3 Reliable Application

Pratiksha chaudhary.

• November 23, 2023

Table of Contents

Invisible ink, often referred to as security ink or sympathetic ink, is a writing ink that is initially invisible when applied and can subsequently become visible with the use of heat or UV light. Steganography comes in the form of invisible ink.

What actually is invisible ink?

Invisible inks for use with invisible ink pens are formulated using ingredients such as sodium hydroxide and thymolphthalein. These inks come in a variety of forms, including UV- and heat-activated inks. Once inscribed, the message becomes invisible and may be broken using chemicals, heat, or UV light.

The process of turning invisible ink visible might involve adding heat, using a specific chemical, or employing UV light, depending on the kind of chemical reaction the ink is based on. The hidden message is eventually made public as a result of all these unique treatment.

History of invisible ink

Invisible ink has a long history that spans several centuries. It is well known that several chemicals were employed by the ancient Greek, Roman, and Chinese civilizations to convey concealed messages. Using milk, lemon juice, or natural pigments that were visible when heated or exposed to certain substances was one technique. A lot of people started using sympathetic inks throughout the Renaissance. These inks could only be seen in specific situations, such when a reagent was applied. More advanced invisible inks were created in the eighteenth century by well-known people like Sir George Lewis, who used chemical processes to expose letters.

During both World Wars, invisible inks were used for espionage. Contemporary versions are still used for novelty and security applications.

Chemistry behind invisible ink

The sort of invisible ink that is utilized affects its chemistry. Here are few instances:

• Heat-Activated Inks: – Organic ingredients like milk and lemon juice are frequently employed. These substances go through chemical processes that result in the manifestation of the concealed message when heated.
• UV-Activated Inks: – Substances such as luminous materials can be utilized. These substances glow when exposed to ultraviolet (UV) light, revealing the secret information.
• Chemical Reaction Inks: – Phthalein and thymolphthalein are examples of compounds that are sensitive to pH variations. Applying a basic solution, such as baking soda solution, causes the ink to change color and show the message.
• Iron Gall Inks: – Age-old inks used for long-term writing Tannic acid, derived from plant extracts, reacts with iron sulfate to form a whitish substance. Air exposure causes it to get black over time.

Properties of invisible ink

The properties of invisible ink are:

• blends with water.
• Non-volatile, meaning it doesn’t smell strongly.
• not leaving crystals on paper, that is, difficult to notice in passing light.
• invisible to UV light.
• doesn’t discolor or break down the paper, like silver nitrate.
• Nonreactive when exposed to iodine or any other common developer.
• The ink should have as few potential developers as feasible.
• shouldn’t grow in a heated environment.
• simple to attain and has the potential for at least one harmless usage by the possessor.
• Not a mixture of different compounds, since this would go against rule number 7.

Advantages of using invisible ink

The advantages are discussed below:

• Using a cotton swab, stamp, fountain pen, toothpick, calligraphy pen, special purpose stylus, or even your finger immersed in the liquid, you may apply invisible ink to a writing surface. When dried, the written surface has the same texture and reflectivity as the surrounding surface, giving the impression that it is blank.
• Additionally, there are toy invisible ink pens with two tips: one for writing with invisible ink and another for ink development. A “decoder pen” is usually included to expose the invisible portions of texts or photos, answering questions written in conventional ink or filling in blank areas in pictures. Invisible ink is occasionally used to print portions of pictures or text in books for kids to play with.
• Important home objects are frequently discreetly marked with security marker pens or UV markers, which have fluorescent ink that glows when exposed to UV light, in case of a theft. Specialty security marker pens are available that are designed to write on non-porous materials like metal, glass, and plastic. With the use of a blacklight or another UV light source, the mark may be read. Commercially available, security marker pens are frequently utilized as a deterrent to crime.

• Kristie Macrakis (2015).  Prisoners, Lovers, and Spies: The Story of Invisible Ink from Herodotus to al-Qaeda . Yale University Press.  ISBN   978-0300212600 .
• John A. Nagy (2009).  Invisible Ink: Spycraft of the American Revolution . Westholme Publishing.  ISBN   978-1594161414 .

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Make invisible ink

Use invisible ink to write your own secret messages!

Mix equal amounts of baking soda and water in a small cup.

Write your secret message on paper using the mixture and the paintbrush.

Wait for the paper to dry, then pass the note to your friend.

To reveal the message, use a sponge or brush to paint the paper with grape juice.

WHAT'S HAPPENING?

The slight acidity of the juice reacts with the baking soda to reveal your message.

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Making Invisible Ink Appear

Invisible ink isn't just something you see in James Bond movies or X-Files re-runs. Even Harriet the Spy has her own invisible ink pens. In fact, prisoners of war used their own sweat and saliva as invisible ink.

The way invisible ink works depends on the method used to make it. There are several ways to make invisible ink and below you will find a few different recipes for making your own invisible ink and how it works.

Invisible Ink the Baking Soda Way

• Mix about 1/4 cup (60 ml) of baking soda and 1/4 cup (60 ml) of water.
• Next, write using a Q-tip, toothpick or brush on a piece of paper.
• Let it dry completely.
• To read the secret message , paint grape juice concentrate across the paper with a paint brush or a sponge. Don't forget - grape juice stains.

Why it works: Grape juice has an acid that reacts with the baking soda. A different color appears wherever the secret message is written .

Invisible Ink the Milky Way

• Put a little milk in a small bowl.
• Write with the milk on a piece of paper with a Q-tip or a brush.
• Let your message dry completely.
• To read the message just heat the paper. Use an iron or 100-watt light bulb or stove element. Don't rest the paper on the bulb.
• Ask an adult to help in case a fire starts and never use a halogen light .

Why it works: Milk is an organic product which means it comes from a living thing. When it's heated, it burns at a slower rate than the paper. Your invisible message shows up brown.

Invisible Ink the Lemon Way

This works the same way as the Milky Way .

• Simply dab a Q-tip or brush into a bowl of lemon juice and write away. Just make sure you don't use too much.
• To see the message, simply heat the paper after it dries.
• Another way to see the message is put salt on the drying ink.
• Give it a minute and then wipe the salt off.
• Use a wax crayon to color over the message.

Why it works: Both lemon juice and milk are mildly acidic and acid weakens paper. The acid remains in the paper after the juice or milk has dried. When the paper is held near heat the acidic parts of the paper burn or turn brown before the rest of the paper does.

These are only a few ways to make invisible ink . Using the same heat method, you can also use white wine, vinegar , apple juice, and even orange juice, to name just a few. Try some other fruit juices to see what works .

Have Your Say

Do you have your own recipe for making invisible ink? What works best? Let us in on your secret.

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Write Secret Messages Using Invisible Ink Experiment

Be a secret agent and write invisible ink messages using a few basic items you can find around the house in this fun science experiment.

September 2018

You Will Need:

• Lamp/light bulb
• Plain white paper

The Experiment

• Squeeze the lemon juice into a bowl or cup and mix in a few drops of water
• Dip the cotton bud into the mixture and use it to write a secret message onto the white paper
• Allow the paper to dry and the juice to become invisible
• Reveal your secret message by holding it close to a light bulb

The Science

Lemon juice contains carbon compounds that are colourless at room temperature. The heat from the light bulb breaks down the compounds and releases the carbon. The carbon oxidises when it comes into contact with the air and turns brown, making your invisible message visible under the hot light bulb.

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Fire Writing With Invisible Ink

Fire writing is a fun science project. You write a message using invisible ink, let it dry, and then reveal the secret by touching a flame to the edge of the text. The message burns away, leaving the paper untouched except for the fire writing.

Fire Writing Materials

You only need simple materials for this project:

• Potassium nitrate ( buy it or make it yourself )
• Paper (Heavy, absorbent paper works best, but I used ordinary printer paper)

Write a Secret Message

• First you need to prepare your “ink.” Mix potassium nitrate into a very small amount of water. Use just enough water to barely dissolve it.
• Use a toothpick, cotton swab, fingernail, nail, etc. as your “pen.” Start writing the message or design at the edge of the paper. The flame burns in a continuous line, so avoid breaks between words or design elements. Cursive writing works, as do many pictures. You may wish to re-trace the message to make sure it is covered.
• Let the paper dry completely. The message will be invisible.
• Touch the edge of the paper where the message started with a flame from a lighter or match. The flame will burn away the message, leaving the rest of the paper intact.

You’re writing with fire, so use common sense and be prepared to extinguish the paper if the project gets out of control. This project is intended for responsible adults.

How It Works

Invisible ink works by subtly changing paper so that the message disappears when the ink dries but is revealed by a chemical or heat. Most chemicals used as invisible ink (e.g., lemon juice, saliva, vinegar) damage the paper. When the paper is exposed to heat from a light bulb or blow dryer, the damaged part darkens more than the untouched paper so the text appears. Theoretically, fire writing works with any message written with this type of invisible ink. But, there is a real risk of burning the entire paper and not just the message! This project uses potassium nitrate because it burns more readily than paper. The message burns away quickly enough to preserve the paper.

Looking for more fun? Give pyrography a try. This is a type of fire writing done using a sparkler.

Related Posts

Invisible Ink Lab - True Experimentation for the Start of the School Year

Introduction: Invisible Ink Lab - True Experimentation for the Start of the School Year

This lesson is appropriate for middle school science students in class sizes up to 20 students (more if you have additional support in the classroom).

Kids love to experiment. Give them some baking soda, vinegar, lemon juice, and various other sundries and they will mix and match and explore every possible outcome. Isn't that what experimentation is? Exploring all of the various outcomes so that a hypothesis can be supported by conclusive evidence? Well, maybe giving kids a pile of supplies and letting them have at it isn't quite the true type of experimentation we want to harness in the middle school science classroom. So how do we get kids excited about experimentation while still giving them the ins and outs of the scientific method without making it seem like a humdrum step-by-step procedure when science is anything but a humdrum step-by-step, paint-by-number practice? I have found that this lab meets many of those requirements while really sparking the scientist that is innately in each and every child.

The problem given to the students is simple... "which household liquid; vinegar, milk, lemon juice, makes the best invisible ink with exposure to heat?" Students are then given the task to go through a somewhat rigid set of steps to help them determine which of the three liquids works the best based upon qualitative observation. The lab requires basic supplies and tools and can be accomplished easily in 1-1/2 class periods (about 90 minutes).

White Distilled Vinegar

Milk (whole, 1%, 2%, etc...)

Lemon Juice Concentrate

Plastic containers

Electric hotplates / burners

Test tube clamps or tongs

Invisible Ink instruction sheet / Lab sheet

Invisible Ink student lab sheet

Invisible Ink test strips

Step 1: Get the Materials Together and Ready for the Lab

Warning - This lab does involve the use of hot plates in the classroom and paper being put near the hot plates (on low). I have completed this lab with sixth through seventh grade students for the past three years and have had no problems. This is after a very lengthy discussion on proper lab safety, classroom etiquette and behavior, and the almighty riot act. I only run three burners at a time in one set location and have water near by just in case a kid needs to dip their test sample (if it's smoking). I also monitor the entire area like a hawk.

You will need only a small amount of liquids for the lab since the students will be using such a small amount for their testing. I usually have the lemon juice and vinegar in the supply closet and bring in a cup or two of milk from home on the lab day. You will need some type of holding mechanism for the paper slips. I have a large number of old test tube clamps that I use and they work perfectly. As for the burners, ceramic burners are the best choice as they typically will not ignite paper quickly unlike coil burners which ignite paper very fast. I use a bunch of recycled cookie containers for the water dunking areas and for organizing the supplies for each table.

Step 2: Set Up Supplies

Instead of writing the names of each liquid on the cups I create a simple key that is written on the board where a letter represents each liquid. You will need four cups for each group. One for each liquid and one for the discard container. Pour in a small amount of liquid into each dixie cup with the letters marked on them and place them, along with three q-tips, into the plastic containers to be easily distributed to the class.

Step 3: Day #1 - Set Up and Preparation

You will need to make sure to print all of the lab materials I provided in the supplies section at the start of the instructable. Print a classroom set of the lab instruction sheets, so that each student can use one throughout both days of the lab. Print off one copy of the student sheet for each student you plan on completing the lab with and print off one set of test strips for each group.

Distribute the instruction sheet first and take the time to review it with the students, making sure to stress the importance of them following the directions carefully and completely during the entire lab. After you feel confident that your students know the expectations and are prepared for the lab you can distribute the test strip sheets to each group. Hand out a set of scissors to each group so that they can cut them apart and make sure that they are properly labeling the sheets based upon the directions in the lab instruction sheet. You can then distribute the lab supplies to each group so that they can write their group number on the test strips they have set up. This entire process will take approximately 35 minutes and combined with a lab safety lesson and review of the directions before starting it will take an entire class period. This is perfect since it allows the strips to dry overnight. Let them dry as much as possible before having the students paper clip their group's strips together for the next day.

Step 4: Day #2 - Experimentation!

The next day is where the lesson really shines. Before you get too excited about exposing the hidden messages you should hand out the student lab sheet to each student and review the requirements for the lab sheet. I use a standards based grading system with a grading scale I created (the speedometer) but you are welcome to change things up if it works better for you a different way. I typically will take the time to review exactly how I want the information to be detailed in the data table and I will do a short explanation of what it means to use the data table as evidence for the three focus questions on back.

Once the kids are all set with the lab sheet you can hand back their now-dried test strips and have them fill out the first section in the data table comparing the three samples to each other to determine which one is the most invisible at the start. I will typically put two groups at each burner station so as not to crowd them but if you wanted you could have specific students from each group come up to expose the invisible ink and maybe have three groups at a time... you'll have to feel it out. Review the directions of how to expose the message on the invisible ink test strips and make sure that the students understand that the first exposure is for ten seconds, the second for ten additional seconds, and the third for twenty additional seconds. You will definitely see the kids getting into the lab and getting excited about the invisible ink showing up with the heat. I always have kids that ask me if other liquids would work and I have encouraged them, with parent help, to try it at home with a light bulb, hair dryer, toaster oven, or other heat source (once again, with parent support). The lesson leaves multiple avenues to head towards when it comes to reviewing the lesson and discussing the results. I typically will use this presentation to help stir up more discussion and help us segue into our next experiment-based project. I hope you enjoy the lab and please post any comments or teacher notes if you use the lesson.

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Invisible Ink Experiment

Have you ever tried making invisible ink? The Invisible Ink experiment shows you how to do it.

This article is a part of the guide:

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Would it not be cool to pass on secret messages only you and your friends can read? Invisible ink is fascinating, not just for kids but for everyone who is young at heart! You can actually get them from kiddie stores and other fun prank stores. But few people know that we can make invisible ink just by using materials that can be found in our very own kitchen!

There are a lot of ways on how we can create invisible ink. But for this Invisible Ink experiment, we will make use of the following materials:

• Clean paintbrush or cotton swab
• Desk lamp shade/light

This experiment is very simple, yet very fun to do! Make sure you brought with you your friends so you can all try making invisible ink and at the same time exchange invisible messages!

First step is to get milk and dip your clean paintbrush or cotton swab in it, and using this as your ink. Write on the clean sheet of paper with the 'inked' paintbrush or cotton swab and allow it to dry. To read the hidden message, you'll have to apply heat to the paper. Turn on your desk lamp and hold the paper close to the light bulb, allowing the light bulb to heat the paper. The heat from the light bulb will cause the writings to darken, allowing you to read the invisible writings!

There are several other materials you can use in the absence of milk. You can use lemon or lemon juice, baking soda mixed with water, vinegar or even grape juice. Basically, just anything acidic can be used as invisible ink. Also for the heating agent, you can make use of other heat sources such as sunlight or gas stove. However, you'll need the supervision of your parents if you are to make use of a gas stove as source of heat for this experiment.

Milk, lemon, vinegar, grape juice or any other acidic liquid, weakens the paper when applied. When you apply heat to it, the portion where you wrote your message oxidises and burns faster than the surrounding paper dry from the ink. The said portion will turn brown, thus revealing your secret message.

There is another way to decode the secret message and make it appear, without having to apply heat. You can do this by putting salt on the ink after writing on the paper. Wait for about 60 seconds before you wipe the salt off the paper and then colour over the writing with a crayon. See the message appear!

You can also reveal the message by applying grape juice over the message. Notice that the writings will change in colour when grape juice is applied!

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Explorable.com (Jan 22, 2011). Invisible Ink Experiment. Retrieved Sep 16, 2024 from Explorable.com: https://explorable.com/invisible-ink-experiment

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