You may remember those cardboard magic glasses from your childhood, that could display invisible messages that you alone were able to read. This technology is now available in the form invisible ink pen, which allows you to secretly write messages that can only be read with certain types or heat. This technology could be used in many situations, such as preventing roommates to read your private social media passwords or keeping snooping colleagues at bay.
Depending on what you want to do, there are several chemicals that can be used for invisible ink. For example, some inks that change color when exposed to heat can be read by placing a piece of paper on a radiator or iron, using a hair dryer, or even exposing it to a 100-watt light bulb. Other inks can be made visible by a light, such as laundry detergents, soaps, and even human saliva. Other organic fluids, such as alcohol or methyl ethylketone, that oxidize with heat 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 glasses are great for revealing inks that depend on fluorescence or luminescence. However, regular white lights won’t 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. Use of code words such as “heat” and other unusual words out of context can also raise suspicions.