You may remember the cardboard magic glasses that you used to use as a child. They displayed invisible messages which only you could read. Invisible ink pens are a new technology that allows you to write secret messages which can only be revealed by certain types of heat or light. This could be useful in a variety of situations, from preventing roommates from reading your private social media passwords to keeping snooping coworkers at bay.
Depending on what you want to do, there are several chemicals that can be used for invisible ink. Some inks can be read using a hairdryer, a radiator, or a piece on paper that changes color when heated. Other inks can be made visible by a light, such as laundry detergents, soaps, and even human saliva. Lastly, organic fluids that oxidize when exposed to heat, such as alcohol and methyl ethyl ketone, are also used.
You will need to use a special type of light which reacts with the chemical components in the ink in order to see it. UV protection glass is the best way to reveal inks that rely on fluorescence and phosphorescence. White lights, however, will not work. A black light will reveal inks which rely on chemical processes such as chemiluminescence.
There are some telltale signs that can alert a censor of the presence of invisible Ink. For example, pen scratches caused by a sharp tip and a change in reflectivity due to acidic ink. The use of key words like “heat” or any other unusual code word in an out of context could also raise suspicions.