Ever Wonder How Invisible Ink is Decoded?

Invisible ink is a topic that is both fascinating and rich in history. Undetectable by the naked eye unless accompanied by its activator (e.g. fluorescent lights, heat, lights bulbs, etc.), invisible ink is typically transparent right at printing, or very soon after. With a variety of uses, from security measures on money, to printing of official document, to fun activities for kids, invisible ink serves many purposes.

One interesting example comes from none other than the CIA. According to classified documents going all the way back to World War I that were recently released by the government, invisible ink played an important part of our espionage efforts during the war:

“Nearly 100 years after these memos and instructions were written for spies, generals and diplomats, ordinary citizens can finally learn how to open sealed envelopes without detection, concoct “German secret ink” and write invisible messages”. (Source: History.com article from April of 2011).

Let’s explore the different types of invisible ink activators (i.e. decoders), including organic based and chemical based, and explain how each works. As we mentioned, the activator is the key component to deciphering messages written with any kind of invisible ink. There are the 3 main types of activators. Let’s start with heat.


Heat activated invisible inks are made with any sort of acid-based fruit juices such as lemon juice, onion juice, and even baking soda. After application of the acid based fruit juice you just simply need to add some heat to reveal the message. Heat can be applied by any one of the following methods: ironing the paper, set it on a hot radiator, place it in an oven (set lower than 450° F), or hold it up to a hot light bulb.


Chemically activated invisible inks tend to get a little more complicated because you have to know the exact activator that will set off the reaction and reveal the message. According to Wonderopolis.com, “Chemically-activated inks can be made from any two chemical substances that are colorless until mixed with one another. When the message receiver adds the second chemical developer, the chemical reaction between both substances causes the color to change and the message to appear.” Pretty cool stuff. Makes you wish that you would have paid more attention in science class.


Light activated ink works because it contains substances that glow under different types of light (typically a black light) but remain invisible to the naked eye. Light activated invisible inks are a favorite of amusement parks and clubs because they can simply stamp the hands of patrons with the invisible ink that is then activated by a fluorescent light. If you have ever been to one of these establishments it’s more than likely that you’ve already come into contact with this type of invisible ink.

You are now officially an invisible ink expert! Ok, ok, maybe not an expert. But in case you're ever on Jeopardy, at least now you'll know the 3 main types of invisible ink activators.



If you’re ever in need of ink that can actually be seen and read by humans without the need of an activator, please check out our site or give us a call at (888) 311-2828 if you have any questions.