What is the cyanotype printing process?

The cyanotype is a slow-reacting photographic printing process that uses iron salts to produce monochrome prints in distinctive shades of Prussian blue. Introduced in 1842 by Sir John Herschel, it relies on light-sensitive chemicals exposed to ultraviolet and blue light, and requires only water for development and fixation. While historically famous for architectural blueprints, it remains popular in art and photography today.

What we know

• The cyanotype process uses two primary chemicals: ferric ammonium citrate or ferric ammonium oxalate, combined with potassium ferricyanide. [2]
• The mixture is sensitive to a limited near-ultraviolet and blue light spectrum ranging from 300 nm to 400 nm, known as UVA radiation. [2]
• Development and fixation of a cyanotype print require only water. [2]
• Sir John Herschel introduced the cyanotype process in 1842. [2, 5]

Where to go next

• whoWho was Sir John Herschel?
• what followedHow do architectural blueprints work?
• the bigger pictureWhat are other sun printing techniques?
• a case in pointHow did Anna Atkins use cyanotypes in botany?
• compared withWhat replaced traditional blueprints in industry?
• an unexpected connectionHow did a photographic process become a botanical book milestone?Botanist Anna Atkins utilized the cyanotype process to publish the first book illustrated with photographic images.

Sources

• [1]cyanotype (Wikidata Q372532) · CC0 1.0
• [2]Cyanotype · CC BY-SA 4.0
• [3]Anna Atkins · CC BY-SA 4.0
• [4]Sun printing · CC BY-SA 4.0
• [5]Blueprint · CC BY-SA 4.0