Invisible ink
Invisible ink is a type of liquid that cannot be seen or read unless it is first activated. Chemical reactions, heat, ultraviolet light or special glasses are used to make invisible ink visible.
It is used to send secret messages or for entertainment. Invisible ink pens are sometimes sold or used for prizes, usually with an ultraviolet light.
More reading
- Iggulden, Hal; Iggulden, Conn (2007). "Secret Inks". The Dangerous Book for Boys. New York: HarperCollins. p. 149. ISBN 978-0061243585.
Invisible Ink Media
A coded letter from Benedict Arnold, originally written in invisible ink. Handwriting by Peggy Shippen Arnold is interspersed with coded communication in Arnold's hand.
A common task in escape rooms is assemble an eye-safe blacklight torch to reveal messages in invisible ink
A US$20 bill showing a visible stripe under an ultraviolet light
