Posted by Adam Quinan on October 09, 2003 at 01:29:06 from 66.185.85.76 user Adam.
In Reply to: Photography in Coot Club posted by Andrew Craig-Bennett on October 08, 2003 at 23:51:39:
I can't tell you how common home developing was in the 1930s but as for the "fixing" of the contact print, Dick would have had to dip the paper into a solution of sodium thiosulphate.
Basically photography works because the film contains a silver salt which when exposed to light changes to another silver compound. A developer solution is then used on the film which changes the exposed silver salt to metallic silver which appears black on the negative. Hence Pete's N***** comment. The fixer is the final step which removes the unexposed silver compound leaving it a clear film.
Making a print is similar you shine the light through the negative and the silver salts in the paper change and are removed in a similar manner by another developer. So what is black in the negative casts a shadow which is therefore white on the paper. The fixer then dissolves away the spare unexposed silver salts to stop it turning black.
I hope this is clearer than mud or Dick's over exposed contact print.
Photographic developers can make a good deal of money recovering the silver from the used developer and fixer chemical waste.