[pure-silver] Re: Non-acid rapid fixer - continued

  • From: "Richard Knoppow" <dickburk@xxxxxxxxxxxxx>
  • To: <pure-silver@xxxxxxxxxxxxx>
  • Date: Mon, 22 Feb 2010 13:30:51 -0800

----- Original Message ----- From: "Lloyd Erlick" <lloyd@xxxxxxxxxxxx>
To: <pure-silver@xxxxxxxxxxxxx>
Sent: Monday, February 22, 2010 12:05 PM
Subject: [pure-silver] Re: Non-acid rapid fixer - continued

February 22, 2010, from Lloyd Erlick,

six minutes in each bath, so a total of twelve minutes, at normal processing temperature (for me, 21C).

same for film and FB paper. (Not the same batch of fix, though ...)

I don't test prints or fixer, I'm afraid. I never let my fixer come close to exhaustion, I never keep it around more than a few days after mixing it, and for important work I make up fresh fix and change it often. Excuses, excuses.


Something else of importance: The ability of a fixing bath to make the insoluble remaining silver halide soluble in water requires about three thiosulfate molecule for each silver halide molecule. If there is not enough free thiosulfate in the fixer it can't do a complete conversion. Some of the halide will be converted to insoluble or only partially soluble silver-thiosulfate complexes. The halide is _never_ fully converted no matter how long the emulsion remains in the fixing bath. In a two bath system the second bath will clean up the insoluble complexes left by the first bath, provided it is not worked to the point where it also has not enough free thiosulfate ions in it. Testing the first bath is probably also a reliable test for the second. The complexes in incompletely fixed emulsion change slowly with time to a form which can no longer be converted by subsequent fixing. The reaction takes about two weeks. Michael Gudzinowizc wrote extensively on this in the rec.photo.darkroom news group some years ago. He gives very full explanations of both fixing and the effects of incomplete fixing. A google search should still find the stuff. Kodak Research Laboratories also published extensively on fixing chemistry. Because Kodak chose to publish its research papers in established, peer-reviewed, journals, rather than in a house organ, the material is somewhat scattered. However, most of it was covered by the _Journal of the Society of Motion Picture and Television Engineers_ in its various versions. Other sources are the _Journal of the Franklin Institute_, the _Journal of the American Chemical Sodiety_ and others but JSMPTE will find most of it.

Richard Knoppow
Los Angeles, CA, USA
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