Also called “coin revelable inks” in Anglo-Saxon language, these invisible inks are often used in mail order, various games and even in security to reveal a hidden word.
After printing and the invisible ink has completely dried, it is revealed by simply rubbing the print using a coin (preferably brass or copper). The pattern changes irreversibly from colorless to more or less dense gray. These inks come in offset, letterpress and flexography formulations.
