Quote Originally Posted by Photo Engineer View Post

Most silver has impurities in it that will make it unusable for photographic emulsions. It would depend on the silver and on the nitric acid. Reaction of silver metal with nitric acid IIRC, requires red fuming nitric acid as silver is a noble metal. RFNA, as it is called, is rather hard to get and gives off very toxic fumes.

Two questions:

1. Is there some way to test the emulsion suitability of a particular source of silver nitrate before actually putting it to the pudding test? If the seller claims 99.8% (concentration or purity, I guess) is this a sufficient or at least hopeful indication? [The claim actually seems a little extravagant to me, but I am not a chemist].

2. I have run across several references to the use of cadmium in discontinued paper emulsions. For example, many photographers liked a Forte paper, which apparently contained cadmium. Do you happen to know the source or sources of cadmium (generally) in an emulsion? In other words was it cadmium nitrate or cadmium bromide or some other source? And at what step in the emulsion making process was it introduced into the emulsion?

Well, I guess that's 2.5 questions. How many am I allowed?

Thank you! --Joe