How to Make an Invisible Ink Pen

Co-authored by wikiHow Staff

Last Updated: February 14, 2023 References Tested

Invisible ink is fun and exciting to use. You can send secret messages to your friends and family using ingredients that can be found lying around the house. There are many different solutions that you can use as ink and even more options for how to reveal the message. Any liquid that is slightly acidic can be used as invisible ink. With a little bit of heat, you can reveal all of the secrets!

Method 1

Method 1 of 3:

Using an Acidic Solution

1
Gather the necessary materials. To make an invisible ink pen, you will need Q-tips or a paintbrush, an acidic solution, a shallow dish or bowl, white paper, and a source of heat. The Q-tips or paintbrush will be used to do the actual writing. Choose the item that works the best for you.^{[1]
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- Any of the following can serve as the acidic solution for the invisible ink: milk, vinegar, or lemon juice.
- The heat source can be a candle, a hair dryer, an iron, or even a lamp.
- All of these items should easily be found around the home or purchased at the grocery store.
2
Pour the acidic solution into a bowl. If you are using a lemon, squeeze the lemon until the juice comes out into the bowl. If you are using milk or vinegar, pour about half of a cup into the bowl. The exact amount isn’t important. You will only need enough to write your message.^{[2]
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- Dispose of the liquid down the drain when you are finished.
- Do not use the liquid for anything else once you have used it for invisible ink.
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3
Write on the paper. A Q-tip is a very easy device to use as a pen. Dip it in the solution until it is damp. Write your secret message, dipping the Q-tip into the ink every few letters. This ensures that you have used enough ink for the message to show up later.^{[3]
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- It may be difficult to keep track of what you are writing because the writing will be invisible as well. If you write at a well-lit table you will be better able to see what you are writing while the ink is still wet.
4
Let the ink dry fully. Before revealing your hidden message, you need to let the ink dry completely. It shouldn’t take more than 30 minutes for the ink to finish drying.
- Set the first paper aside and write more messages while you wait for the first one to dry.
5
Apply heat to the paper. Once you have obtained a heating device, apply it to the paper where something has been written with the invisible ink. As the paper heats up, the areas that have invisible ink on them will begin to turn brown. When the message starts to appear, remove the heat source from the paper. If the message is unclear, keep the heat on for a few more seconds until it comes clear.^{[4]
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- Be extremely cautious not to light the paper on fire if you are using a candle. Adult supervision is recommended for this to avoid burns or other injury.
- If you are using a hair dryer, use the low heat seating and wave it across the paper until the words appear.
- If you are using an iron, use it on a low setting. To avoid burning the paper away, place a piece of parchment paper between the iron and the paper before rubbing the iron on top.
6
Reveal the writing with salt. You can tweak this method a little bit by using salt instead of heat to reveal the message. When the ink is still wet, cover it in salt. Let the salt sit for at least two minutes and then brush it away from the ink. Let the ink fully dry and then color over the message with a wax crayon.^{[5]
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- The wax will not stick to the salt in the ink and you will be able to read what is written!
- There is no exact amount of salt to use, just make sure the message is covered completely while the ink is still wet.

Method 2

Method 2 of 3:

Using Petroleum Jelly as Invisible Ink

1
Gather the necessary materials. Petroleum jelly is a fun ink to use because it will glow in the dark under a black light (UV light). To use this type of invisible ink, you will need petroleum jelly, Q-tip cotton swabs, white computer paper, and a black light.^{[6]
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- Most of these materials should be easily found around the house.
- You can purchase a black light at a local superstore or online.
2
Write on the paper with the jelly. Dip the cotton swab into the petroleum jelly until you have a small amount on the end. You don’t want a big glob of it because that will be difficult to write with. Write your message with the tip of the cotton swab.^{[7]
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- For best results, try to make the writing smooth, avoiding bumps from the jelly.
3
Shine the black light on the paper. To reveal the written message, shine a black light on the paper. You can even turn the normal lights out or look at it in a dark closet. The words you wrote will glow in the dark under the black light.^{[8]
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- You don’t have to wait for the jelly to dry completely before revealing the message.

Method 3

Method 3 of 3:

Writing with Baking Soda

1
Gather the necessary materials. For this type of ink, you will use baking soda for writing and grape juice to reveal the hidden message. To do this, you will need ¼ cup of water, ¼ of baking soda, Q-tips, grape juice concentrate, and a paintbrush/sponge brush.^{[9]
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- All of these items should be found around the house or purchased at the grocery store.
2
Dissolve the baking soda in the water. Pour the baking soda into the water and stir until it is fully dissolved. The baking soda will dissolve faster if you use warm water. This solution will serve as the invisible ink for your secret messages.^{[10]
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- The exact amounts of baking soda aren’t important as long as you have equal amounts of baking soda and water.
3
Write your secret message. Dip the Q-tip into the baking soda solution until the tip is damp. As you write, you will need to dip the Q-tip into the solution again to make sure you have enough ink. It can be hard to see what you’re writing because the ink is invisible.^{[11]
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- While the ink is still wet you can see it if you are working in a well-lit room.
4
Set it aside to dry completely. The ink must dry completely before you try to reveal it or the reaction will not work. Put your papers off to the side and write more messages while the first ones dry. The ink shouldn’t take more than 30 minutes to dry.^{[12]
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- When the ink is fully dry, you won’t be able to see anything on the paper. It will look like a normal blank sheet of paper.
5
Brush the message with grape juice. Once the writing has dried completely, you can reveal your message. To do this, dip a paintbrush in grape juice and brush it across the message. When the message is covered in grape juice, the writing will change color and you will be able to read what is written. This works because grape juice is acidic and reacts with the baking soda in the invisible ink to change color.^{[13]
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- Avoid getting the grape juice on your clothes because it can stain.

Community Q&A

Question

Is there something I can use instead of the grape juice?

Community Answer

Yes. Lemon juice or vinegar should also work.
Question

Where can I get petroleum jelly?

Lexi Gen13

Community Answer

You can get petroleum jelly at any drug store such as CVS, Walgreens, or Target. Petroleum jelly is also called Vaseline.
Question

What can I use instead of acid and how do I fill that ink in the pen?

floortjj1

Community Answer

Lemon juice or vinegar should work. For the pen, maybe you could take an empty pen and try adding the ink with a syringe.