What is "cyanotype"

Cyanotype \Cy*an"o*type\ (s?-?n"?-t?p), n. [Cyanide + -type.] A photographic picture obtained by the use of a cyanide.

n. 1 (context uncountable English) An early photographic process employing paper sensitized with a cyanide. 2 (context countable English) A photographic print produced by means of this process.

Cyanotype is a photographic printing process that produces a cyan-blue print. Engineers used the process well into the 20th century as a simple and low-cost process to produce copies of drawings, referred to as blueprints. The process uses two chemicals: ammonium iron(III) citrate and potassium ferricyanide.