That is Invisible ink, also known as security ink or sympathetic ink, is a substance used for writing, which is invisible either on application or soon thereafter, and can later be made visible by some means. Invisible ink is one form of steganography.

Invisible Ink uses PicoWay laser technology, which aims to shatter the tattoo ink, but leaves the surrounding skin intact. At Disappearing Ink, costs range between $100 and $400 per session, averaging around $200 per session, Wes South said.

Once the message dries on the paper, it is invisible. When the ink is exposed to heat, such as under an iron or over a candle flame or 100-watt light bulb, the acids in the liquid turn a different color and the message becomes visible. ... Another type of invisible ink is chemically activated.

Written by

Boby Sharma

From team reformer.