Invisible ink
substance used for writing which is invisible and can later be made visible
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
change- Iggulden, Hal; Iggulden, Conn (2007). "Secret Inks". The Dangerous Book for Boys. New York: HarperCollins. p. 149. ISBN 978-0061243585.
