[alt-photo] Re: tintype
zphoto at montana.net
Wed Nov 3 17:51:10 GMT 2010
OK finally talked with Rockland. I called sales and not technical help--that was the trick :)
Packet 1. Dektol
Packet 2. sodium sulfate
Sol 3. IS 50% ammonium thiocyanate.
So we'll see how it goes tomorrow with 18 students learning this process at once--with digital contact negatives no less :)
PS Etienne, I reread your post and now realize you did know it was all mixed together--sorry for the confusion of my last post. But what you said seems accurate given what I have seen of tintypes and their characteristic whiteish appearance. Thanks.
Etienne said <cut>:
While Rockland describes its tintype developer as a "reversal developer," tintypes and ambrotypes (like Daguerrotypes) do not actually use reversal processing in the traditional sense of the term. The silver deposits remain negative (i.e., more silver where there was more exposure). The apparent positive "reading" is caused by the black backing and by development that causes the silver deposits to look more whitish than the normal black silver deposits we are familiar with. In the wet-plate collodion process, this is usually accomplished by developing with ferrous sulfate. I think the Rockland kit provides thiocyanate (or maybe tries to get by with thiosulfate) as a developer additive to keep grain size small and promote whitish silver deposits.
Thiocyanate is also used as a component of "real" reversal developers, to clean up the highlights; and of holographic developers, to keep the grain small. Sodium sulfate is generally used with gelatin emulsions to prevent excessive swelling of the emulsion.
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