Cyanotype is a photographic printing process that gives a cyan-blue print. The process was popular in engineering circles well into the 20th century. The simple and low-cost process enabled them to produce large-scale copies of their work, referred to as blueprints. Two chemicals are used in the process:
- Ammonium iron(III) citrate
- Potassium ferricyanide.
Read more about Cyanotype: History, Process, Toning, Long-term Preservation