Coin revealble inks are often used in security for obtaining the apparition of a hidden message on the original document, and sometimes in Direct marketing.

After printing and drying, this ink is totally invisible, but it is revealed by using a simple coin, (preferably made of copper or brass) rubbed on the printed area. Then the print will appear irreversibly in grey.

Coin revealable inks exist for offset, letterpress and flexography.