Ferric Ammonium Sulfate
Digging around in my stash of photo chemicals, many of which were given to me, I found a jar of Ferric Ammonium Sulfate and was wondering what it was used for. I searched my Darkroom cookbook and really didn't find reference to it. I googled and found that it was used in photography among other things. One link mentioned toners. I suspect it must have been used in iron toners,but another link mention gold toners. I just deciding on what to do with it or if I might have some use for it in the future? Any ideas? JohnW
It was used in the preparation of ferric oxalate developers for dry-plate processes. You can find recipes that included "iron alum" (its pre-systematic name) and oxalic acid: the complex oxalate salts actually involved in development were formed in the bath.
I believe it can be used as an Fe(III) donor in various Van Dyke-like processes as well.
Regardless, the terms to look for in vintage formularies will be things like "iron alum" "ammonio-ferric alum", and similar terms.
If I remember correctly, that was one of the ingredients for Cyanotype.
edit: Nope, my memory failed. That was Ferric Ammonium CITRATE I was thinking about.
Interestingly, while googling this, I ran across a modern lab reference: "iron alum" is apparently still a somewhat-current term in histology. It's used in the converse of a Van Dyke process: silver is deposited on iron-treated fibers that don't readily take silver stain. It amounts, chemically, to the same thing, but it's intriguing to me that there's utility in the procedure diametrically-opposite to what we would use.