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: ferric ammonium citrate and potassium ferricyanide. wikipedia https://www.kunstimunterricht.de/grundbegriffe/techniken/217-cyanotypie.html Favorite