Q&A for How to Make an Invisible Ink Message

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!

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.

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

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

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.

Cranberry juice.

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

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.

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.

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

It should work, but it also depends on the density of the solution you are going to be using and the atmospheric pressure.

Yes, any source of heat will reveal citrus juice.

You could show the process by making a film or time lapse to show how you solved the problem.

You probably can, just as long you still press firmly while writing. Give it a try and see if it works.

Lemon juice can damage a fountain pen by clogging its small pores, which should be conducting the ink, or the acid content might attack the metal parts. As you will probably need only a small amount of lemon juice (unless you are writing a longer text), it seems quite inefficient to empty, wash and dry a fountain pen of ink, then fill it with lemon juice and empty, wash, dry it again afterwards.

Yes. It doesn't change the effect of the ink.

Typically, two or three weeks.

You would hold it there only long enough to make the message visible, usually no longer than a couple of minutes. Holding the paper too long could cause it to catch on fire. Milk and lemon juice messages might disappear again after the paper has cooled, but you can use the heat to make them appear again.

Yes. It works on everything solid.

You could try lime, grapefruit or other citrus fruits, but they will not work as well as lemons.

The milk already saturated the paper, so the juice can't sink in. The juice stains everywhere the milk isn't.

No. The paper will most likely burn and crumble. Try using a candle, a hair dryer iron, or a light bulb.

No, it does not work because it does not generate enough heat to show the message.

Yes you do, or maybe a colored pencil and a normal pencil will come out better. If you are going to use a colored pencil then use a dark color.

Yes, you could, as long as you are using red wine or any dark wine. Clear or light shades will not work.

It depends on which method you try. The last one is super quick, if you want to try that one.

I think so. That's probably a good way to keep secrets. But if the diary's pages are too thin, it might not work.

No, you should use another type of light bulb. LED doesn't work because it doesn't heat up the paper enough.

You can use a marker in place of the white crayon. However, you cannot use a marker in place of the watercolors.

You need a source of UV light, as found in banknote checkers, nail polish curers, black lights or purpose-made UV flashlights. Then, you shine this light on the page and any invisible ink will glow while the UV is being applied to it.