RE: Sources for wet plate collodion chemicals

Richard,

The brightening is in reference to a positive collodion image - tintype or
ambrotype. Positives fixed in hypo tend to have a more muted look compared
to those done in cyanide. Cyanide also gives a warmer "coffee and cream"
tone compared to hypo, which produces a more neutral image. And yes,
excessive fixing in cyanide will erode the image. Cyanide fixing typically
takes 10 or 20 seconds.

I'm still relatively new to the collodion process. I've not tried ammonium
thiosulfate, but I appreciate your comment and will test it.

Kerik

> Long thread snipped.
> I am not a practitioner of Collodion, this is asked out
> of curiousity. My understanding is that wet plate negatives
> were (and are) fixed with a cyanide salt because the halide
> is Silver Iodide, which is slow to to fix in Sodium
> thiosulfate. However, Ammonium thiosulfate is a better fixer
> for Silver Iodide, is it not good enough for wet plate?
> Secondly, I am puzzled by the term "brightening", does
> this refer to the negative or the print? Is it actually
> another term for contrast, some parts of this thread seem to
> suggest it is. Cyanide is a solvent for metallic silver so,
> it seems to me, that excessive fixing in it would destroy
> part of the very fine grain wet plate image. Is this slight
> reduction what is being referred to, and if so, it is
> considered desirable or undesirable?
> If undesirable Ammonium thiosulfate would seem to have
> another virtue beside being relatively innocuous.
Received on Sun Aug 28 10:37:13 2005