How to Make an Invisible Ink Message

Do you want to write your password down so that no one can see it, or do you want to send someone a secret message? Knowing how to make an invisible ink message will have you feeling like a secret agent in no time.

Method 1

Method 1 of 5:
Lemon Juice Invisible Ink

1
Squeeze the juice of half of a lemon into a bowl.
2
Add a few drops of water. Stir the juice and water with a spoon.
3
Dip a cotton swab into the lemon juice mixture and write a message on a piece of white paper. A feather, a toothpick, a fountain pen, a paintbrush or a calligraphy pen will also work in place of the cotton swab.
4
Allow the invisible ink to dry. As the ink dries, your message will disappear.
5
Hold the paper that contains your invisible ink message over a light bulb or flame/candle. Keep the paper near the bulb or flame/candle until the message reappears. Be careful not to put the paper too close if you are using a flame/candle.^{[1]
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Research source
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Method 2

Method 2 of 5:
Baking Soda Invisible Ink

1
Dip a cotton swab into a mixture of 1/4 cup (60 ml) of baking soda and 1/4 cup (60 ml) of water. Use the swab to write a message on a white piece of paper.
2
Wait until the ink is dry.
3
Dip a paintbrush into some grape juice concentrate or any dark juice. Paint the grape juice over your message and wait for the message to appear.

Method 3

Method 3 of 5:
Milk Invisible Ink

1
Dip a cotton swab into a shallow dish of milk.
2
Use the cotton swab to write a message onto a white piece of paper. Allow the milk to dry.
3
Dry the message for about 30 minutes.
4
Expose the message to heat. You can use a light bulb, candle/flame, or an iron. The milk will heat up at a slower rate than the paper, which will cause the message to reappear.^{[2]
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Method 4

Method 4 of 5:
White Crayon Invisible Message

1
Use a white crayon to write a message onto a white piece of paper.
2
Paint over the message using watercolors and a brush. The message will reappear.^{[3]
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Research source}

Method 5

Method 5 of 5:
No Ink Invisible Message

This method relies on pressure and indentation of the paper.

1
Lay out two sheets of paper. Place the first sheet of paper under the second piece.
2
Write your message on the top paper. Do this by applying strong pressure on the pen or pencil.
3
Remove the first sheet.
4
With a pencil, gently shade over the bottom sheet. The message will appear, similar to chalk on a blackboard.

Community Q&A

Question

Are there other ways to make invisible ink?

Community Answer

One other way is to take the highlighting part out of a fluorescent yellow highlighter and leave it in warm water until most of the highlighter is out. Then you can dip a Q-tip in the highlighter water and write a message. Once it dries, turn off the lights, or go into a dark area and take a UV light or blacklight and shine it onto the message. The message will be revealed!
Question

Will a light bulb work, or does it have to be heat?

Community Answer

As long as the light bulb isn't LED, it should generate enough heat to display the message; just be sure not to hold it so close that the paper catches fire.
Question

Could I use a hair dryer as a source of heat?

Community Answer

Yes, but it needs to be on high, and don't hold it too close to the paper or it could catch fire.
Question

Will this really work?

Community Answer

Yes. As you put the paper with the written messages near a open flame, the citrus juices will burn first, revealing the message.
Question

Can I use another color crayon instead of watercolors to reveal the message?

Community Answer

Possibly, but you need to color very lightly. The white crayon blocks the water in the paint from getting into the paper which reveals the message, so if you use crayon, you could accidentally erase the message by coloring too firmly.
Question

What other dark-colored juices can I use other than grape juice?

Community Answer

Cranberry juice.
Question

Can you use lime juice instead?

Community Answer

You can, but it may not show up quite as well as lemon juice.
Question

Do you need to use heat for this to work?

Community Answer

Yes, you need heat in order for the message to appear. You don't necessarily have to use an iron to get the message to appear, though.
Question

How do you know when an invisible ink pen ran out of ink?

Community Answer

When it doesn't work anymore. Shine a light on it (or do whatever you're supposed to do to reveal the ink) to see if the message shows up.
Question

Will anything else work in place of lemon for the lemon invisible ink?

Community Answer

Yes, there are plenty of other methods offered in the article.