Cyanotypes are an early and alternative image processing technique invented 170 years ago by Sir John Herschel in 1842.
The chemicals used are, Potassium ferricyanide and ferric Ammonium Citrate (green)
There are other processes that I have been researching including, salt printing, gum bichromate printing and albumen printing. They all rely at some point having light sensitive elements added to the mixtures to make them work. In a lot of cases that element I silver nitrate a naturally sensitive chemical.
LawriePhoto 