15 Fun Facts About Invisible Ink You Should Notice

We often heard about invisible ink. If you want to create a surprise message for your friends or loved ones, write it using invisible ink. It turns out that this type of ink has a very detailed and unique history!

Invisible ink is usually associated with secret messages. After all, you will need a particular way to read the statements written with invisible ink. And so, here we are going to discuss fun facts about invisible ink!

It is very spy-like and has intrigued people of all ages. If you want to know about how the ink is made or how it works, we will tell you in this article. How difficult will it be to create a fun invisible message using invisible inks? Let’s find out all the fun facts about invisible ink here!

1. What They are Made Of?

What They are Made Of?

How do you create invisible inks? Usually, invisible inks you can find in stores utilize various organic liquid types. However, you can create a secret message at home using easy-to-find materials! For example, you can create hidden messages using orange juice, lemon juice, vinegar, and even coca-cola!

Those kinds of materials will allow you to make invisible ink easily. Even though the message has been obscured, you still want the actual message receiver to be able to read it. The writings will reveal themselves through heat, regular sunlight, ultraviolet light, or chemicals, depending on the type of the invisible inks.

2. How Invisible Ink Works?

Here is another interesting, fun fact about invisible ink! The way the ink work is not that complicated, depending on the materials they use for the invisible ink. Whenever you receive a secret message written using invisible ink, you can try to apply these methods. 

You can expose the message with heat like under hot iron or maybe over the candle flame to read them. The hidden writings will reveal themselves! If the ink uses a particular chemical compound, you may need to use acid. It will turn the ink into a different color visible to naked eyes because of a chemical reaction. Furthermore, you can also use UV light because some inks will reflect a specific wavelength.

3. Secret Communication Among Lovers

Founded as The First Secret Communication

Here’s a little background story about invisible ink. It was the first secret way of communication. According to the Prisoners, Lovers, and Spies: The Story of Invisible Ink from Herodotus to al-Qaeda, written by Kristine Macrakis, the first invisible message was created by a Roman poet, Ovid.

Ovid wrote elaborate instructions about the art of love, the Ars Amatoria. The ancient book stated that characters written in fresh milk are a well-known means of secret communication among lovers. The book also mentioned that you need to sprinkle or rub it with powdered charcoal to read the hidden message. And thus, the first invisible ink was created.

4. As an Entertainment in Eighteenth Century

 Entertainment in Eighteenth Century

In the eighteenth century, the discovery of invisible ink was such a huge phenomenon. It became a new vogue for popular science back in those days. To be specific, it became huge in England and France since they made invisible ink into entertainment. There were even public demonstrations in front of many people. 

5. Some Invisible Ink Can Explode

Can Be Exploded

Did you know that some type of invisible ink may cause an explosion? This accident happened in 1736 to the famous philosopher Jean-Jacques Rousseau. Still, according to Kristine Macrakis, Rousseau was experimenting with some dangerous chemical mixtures to create invisible ink.

Rousseau probably knew the recipe from a book of recreational experiments or a professor friend. So, he experimented with orpiment, a rare mineral that contains arsenic sulfide with quicklime. When Rousseau mixed it, it suddenly fizzed and exploded in his face. Macrakis writes that he swallowed so much orpiment and chalk that it nearly killed him.

6. Invisible Ink in World War I

Used in World War I

This happened when America had just entered the first world war. The Office of Naval Intelligence (CIA predecessor) created instructions on making invisible ink. The secret organization suggested the soldiers use some chemicals and basic materials such as milk and lemon juice to make invisible ink. While the Americans used those kinds of simple materials, the Germans were also pushing the development of advanced invisible ink. 

7. German’s Advanced Invisible Ink

 German Leads the Development of It

As we have mentioned before, the Germans led the development of invisible ink at that time. At the beginning of the first world war, the Germans used inks made from medicine to cure fever and headaches. They also used laxatives. Those types of materials were very inconspicuous, perfect for secret agents. After all, it would not be strange for people to carry medkit.

However, as the war continued, the Allies took secret messages more seriously. They developed inks for particular intelligent-gathering and confidential communication. For instance, the Allies utilized inks made from cobalt salts, copper sulfate, and iron sulfate. They also incorporate advanced reagents to decode the hidden message, such as sodium carbonate, potassium ferrocyanide, and ammonia fumes.

8. Invisible Ink during Cold War

The Use of It was Reduced after Cold War

During the Cold War, the Soviet Union and the West were racing to develop more advanced espionage equipment, including more sophisticated invisible ink. After all, sensitive information was as valuable as nuclear superweapons. In fact, the era was often referred to as the golden age of espionage. The dry transfer method and secret chemical compounds were among the most enigmatic usage of invisible ink.

However, as the Soviets collapsed and the Cold War ended, the number of physicists and chemists that worked on the development of invisible ink was reduced. Furthermore, the discovery of more advanced electronic messaging and digital encryption has significantly diminished the role of invisible ink in espionage.

9. Nicknamed ‘The Medicine’ by Washington

The Medicine

Here is another invisible ink’s fun fact! Do you know that invisible ink was once called ‘the medicine‘? During the American Revolution era, in the 1770s, George Washington utilized secret inks. However, because he didn’t know about the ink’s secret ingredient, Washington referred to the liquid as the ‘medicine.’

The famous Culper Spy Ring, Washington’s secret agents, managed to send confidential information to the first American president through the indigenous usage of invisible ink. They have successfully tracked down the British Army movements and directly sent the sensitive message to Washington!

10. Bacteria Ink in World War II

World War II

The story goes on during World War II. The noble prize winner, Linus Pauling, worked on a wartime project as a chemist. He was in charge of formulating new kinds of invisible ink. He was creating an invisible ink that could resist all known reagents. This way, the enemy would not be able to see the hidden message without the correct reagent.

He and his colleagues experimented with pneumococcus bacteria–inert in invisible ink. The “ink-ified” microbe would react to an antibody and reveal some coloration after being dipped into a dye solution. But, the ink never passed the experimental stage and didn’t make it to the field.

11. Invisible Ink Made from Urine

Invisible Ink Made from Urine

Do you know that invisible ink once used urine as the base material? The Aryan Brotherhood was the one who invented that innovation. In the 1990s, they used juice and urine. They used it as a way to send messages between prisons. T.D Bingham was a Brotherhood Leader imprisoned in Fremont County, Colorado.

He wrote a letter to an outside courier and sent it to the brotherhood members. They were imprisoned in Lewisburg, Penn. The letter was written with urine, and it was about to tell the ‘secrets.’

12. The Best Invisible Ink Material

You might want to know the best material to make invisible ink. The process of making it is actually relatively easy. Yet you can try to make it from lemon juice! That is the best example of an invisible ink material that you can get anywhere. Go try to make a secret message with lemon juice scribbled onto a piece of paper. Another material that you can try must contain an acidic liquid in it. It can be wine, orange juice, onion juice, or Coca-Cola. 

Invisible Ink Material

Another material you can try is vinegar. Vinegar is an ingredient or household liquid you can find at your home. But, it is pretty different from invisible ink made from lemon juice. You will need a chemical reaction to turn the message visible. You can use red cabbage or other strong acidic materials to reveal the hidden message. For example, red cabbage solutions can turn secret notes written with vinegar into a dark red color.

13. Used as Security Ink!

Security Ink!

the current generation, the use of invisible ink has increased in many ways. One of them is the use of it as security ink. You can find it in money. Your paper money has a color shift technology with the help of security inks. The color-shifting inks are used, which cause the note’s color to change when you tilt it.

When we talk about security ink, there are two different types. They are photochromic inks and thermochromic inks. The thermochromic inks can change their color in response to variations of temperature. Separate from that one, the photochromic inks can change their color in response to exposure to UV light.

14. A Non-Toxic Material of Invisible Ink

A Non-Toxic Material of Invisible Ink

If we look into the history of invisible ink, several questions might come up in our minds. One of them must be about its safety. Now you can find invisible inks on a pen or pad in stores. Some of them come with accompanying mini UV flashlight. But is invisible ink toxic? Nowadays, we can find invisible ink markers that are safe and non-toxic. It also has environmentally friendly materials so you can use them freely. 

15. Is It Permanent?


And here is the last fun fact about invisible ink! You can use a pen with invisible ink to write on the skin’s surface, paper, plastics, or even wood. Some invisible ink is permanent and does not wash off immediately. But if you apply it to your skin, it will eventually wear off. If you have already used it on your skin, you might want to try smearing it by rubbing it on some glossy materials. 

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