Cyanotype prints

The cyanotype (from Ancient Greek κυάνεος - kuáneos, “dark blue” + τύπος - túpos, “mark, impression, type”) is a slow-reacting, economical photographic printing formulation sensitive to a limited near ultraviolet and blue light spectrum, the range 300 nm to 400 nm known as UVA radiation. It produces a cyan-blue print used for art as monochrome imagery applicable on a range of supports, and for reprography in the form of blueprints. For any purpose, the process usually uses two chemicals: ferric ammonium citrate or ferric ammonium oxalate and  potassium ferricyanide, and only water to develop and fix. Announced in 1842, it is still in use.