Simple, safe, and a whole lot of fun. Cyanotype was created (discovered) by the English scientist, astronomer, polymath, and all around rad dude, Sir John Herschel in 1842.
Just like a photogram, an image can be produced by exposing it to a source of ultraviolet light (like the sun). The UV light reduces the iron(III) to iron(II). This is followed by a complex reaction of the iron(II) complex with ferricyanide. The result is an insoluble, blue dye (ferric ferrocyanide) known as Prussian blue. Kind of sounds like cyanide, that name should ring a bell. SUPER DEADLY Poison. That being said, the only way to release the toxic is by using sulfuric acid. So don’t do that, oh, and maybe you shouldn’t eat it.
Exposure times range from 5 minutes to 25 minutes, depending on the UV value. You then develop the print in water. The cyanotype is perhaps the safest photo printing method available.
Image by Meghann Ripenhoff