Cyanotype

contact print from old 5×7" glass plate negative, artist unknown image by Uwe Kulick (Image rights)

The cyanotype process is one of remarkable simplicity. It was invented in 1842 by Sir John Herschel.

From 1870 to WWII it was used als "blue print" method to copy technical drafts. The used chemicals aren't silver-based as those of most other photo-chemical photographic processes. Solutions of the method's iron-based chemicals are applied to paper surfaces which become light-sensitive that way. They can be used when they are dried. One amateur's application may be a making simple kind of prints from old large format glass negatives. Of course the results will not be black&white but blue&white since the colour coming out of the development process is prussian blue.