>better than pyro to develop wet collodion, working photographers used iron
>developers almost exclusively as they gave negatives that took far less
>time to print out. It was said that iron developers were only suitable for
>transpaprencies or that they gave dull grey negatives.
According to my notes, iron developers were used for scientific work
because it is the only developer that gives no trace of stain or fog.
Organic materials are now available that are its equal, if not better, for
this purpose.
The only developer I know of (have never used it, but it's in my
experimentation notebook) is a "Ferrous oxalate" Developer (note: not
"ferric"). The formula I show is:
25% solution ferrous sulfate 1 part
25% solution potassium oxalate 3 parts
The ferrous sulfate solution does not keep if exposed to the air, so the
solution must be kept in small glass bottles (preferably with "1 part" of
whatever quantity will be used). The two solutions should be mixed just
before processing, with the ferrous sulfate added slowly to the oxalate
(otherwise, an insoluble precipitate will form). Negative exposure should
be about 4x normal. The formula does not use potassium bromide, but a
"couple of drops" may be added to minimally correct overexposure. If the
image has a deposit of a white substance, that is calcium oxalate, so
calcium-free water must be throughout the process, including washes and
fixer. Should there be such a deposit, a 0.5% solution of hydrochloric acid
should remove it.
As noted, I never tested it, as I saw no point either then, or now. Modern
developers are of such variety that one can be selected (or created) to do
anything the iron developer can do. If anyone reading this does try it, I'd
like to know the results.
Sil Horwitz, FPSA
Technical Editor, PSA Journal
silh@iag.net