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The dyes used in the disappearing ink you’re buying from your local store are non-toxic. You’re likely not exposed to any health and safety risks by being in physical contact with the disappearing ink.
However, if you’re considering making invisible ink, you may need some supervision. Disappearing ink is made using lye which can be extremely dangerous and caustic. Additionally, the disappearing ink itself can be toxic if it’s ingested, so you must ensure that you keep it away from your mouth and eyes.
If you’re ever joking around with a disappearing ink pen, make sure that you don’t accidentally spray it in someone’s eyes.
What Is Disappearing Ink?
Inks visible for a while and then disappear are called invisible or disappearing inks. Children generally use these inks to prank their peers in modern times. However, these inks were used to relay secret information during World War I days. Invisible ink is a form of steganography. Steganography is a way of hiding a secret message in things that aren’t a secret.
Types of Invisible/Disappearing Inks
If you’ve ever seen an invisible ink, you have likely seen the one that disappears after a while. It’s one of the most common ones that you’ll witness. These inks are readily available, so they’re the ones that everyone has seen.
1. Inks Developed By Heat
These invisible inks are heat-activated, which means the presence of heat will make the words or images drawn by this ink become visible. It involves an organic liquid or a mixture of organic liquids that become invisible once they dry out. These inks then get oxidized when you apply heat to them and turn brown. As they turn brown, you can read the message written using the disappearing ink pen.
The type of organic liquids you can use may surprise you. The way to go about it is by diluting them in water.
- A cola drink
- A honey solution along with sugar
- Wine or vinegar
- Apple, lemon, orange, or onion Juice
You can use these liquids to write on any paper. However, you need to dilute the liquids first. You will also need to heat the piece for the ink to be visible. You can do this in the following ways:
- You can warm the paper on the radiator
- You can heat it using a blow dryer
- You can use it using an iron
- You can also place it in the oven
Heating the paper should be done at low heat so as not to burn the paper.
2. Inks Developed Using a Chemical Reaction
These invisible inks are chemically activated and thus contain some acid or alkali. These chemically-activated inks generally have two chemicals that are colorless until they are mixed. When the person who wants to read the message adds the first chemical to it, they will find that the chemical reaction between Chemical 1 and Chemical 2 will create a color change and cause the message to appear in full form. An acid-like vinegar is heat-activated. However, diluting the vinegar with red-cabbage water, a spot of chemically activated ink is formed.
3. Inks Visible Under Ultra Violet Light
You have likely seen a lot of examples of these kinds of inks. They’re some of the most popular invisible inks portrayed in media like movies and television shows. These invisible inks tend to glow and fluoresce when you keep them under an ultraviolet lamp. This property is one that many organic liquids share, such as body fluids.
Other invisible inks work differently altogether. These inks tend to absorb ultraviolet lights and don’t fluoresce. You can use these inks on fluorescent paper, and you’ll find that the areas where the ink is present will fluoresce less than the paper which surrounds it. You’ll be able to decipher the words even if the inks are absorbent. Inks that have a yellow tint also tend to share this property. Thus, the two main UV invisible inks have additive and subtractive properties.
You can also see a category of invisible inks when you photocopy the paper. Inks that can be revealed using Ultraviolet light are inks with:
- Laundry detergent
- Body Fluids
- Lemon juice
A lot of amusement parks tend to use invisible ink stamps. These stamps allow you to return to the amusement park even if you’ve left. You can go to an amusement park, and they’ll stamp your hand only for you to look down and see nothing there. However, if you want to return, they’ll get out your hand under a special UV light to check if you were stamped before leaving. They used to follow a visible stamp, but that became too easy to replicate, so invisible ink had to be used.
In popular media like the Oscar-nominated movie “Knives Out,” the late father uses invisible ink to communicate a message to his eldest and only daughter, which she reads using UV light.
4. Inks That Change the Surface of the Paper
This category has all invisible inks. However, you can also use pure distilled water instead. If you apply any fluid to paper, even if it’s invisible, it will alter the paper’s surface. You can heat the paper using iodine crystals, and the paper will reveal itself. Regardless of the writing on the paper, other things change the paper’s surface. Disappearing ink pen strokes and indentations are not things you can hide from the naked eye. Thus, you’ll know when a paper has been written, even if you don’t know what has been written.
5. Disappearing Ink
Disappearing inks and invisible ink rely on a chemical reaction between Thymolpthalein and a sodium hydroxide or potassium hydroxide base. Thymolphthalein is colorless, but when mixed with NaOH, it will turn blue. The base can then react with the Carbon dioxide in the air, causing its pH level to drop, and the ink turns colorless.
Disappearing inks are not toxic unless ingested. If you accidentally ingest the ink, you have to go to a doctor immediately. These inks contain lye which can be dangerous for you if ingested. You should also never try to make invisible ink on your own. Instead, buying one from a trusted store is recommended.