From: Richard Knoppow (dickburk@ix.netcom.com)
Date: 05/19/00-01:40:05 PM Z
At 02:19 AM 05/18/2000 -0400, you wrote:
>> How stable is the pyro stain? Does it fade like the dyes in a color
>negative,
>> or is its stability similar to that of the silver image?
>
>Robert Chapman (or is it Richard Chapman? the one who writes the photo
>chemistry column in Photo Technique, used to be Darkroom and Creative
Camera)
>had an article on pyro stain. According to him, all stain fades and although
>he didn't give a figure, he said that he would not trust the stain for
>critical images.
>
>But I think that since negatives are not the final display products, they
are
>usually stored in the dark, so the longetivity is better. Also, as long as
>the information (the silver density) is preserved, I guess one can always
>make a duplicate negative and develop in pyro again, or I suppose the
>original negative can be bleached and redeveloped in pyro again.
>
>
>Dave Soemarko
I asked Mike Gudzinowicz, an occasional poster to this list and Phd
chemist about this. He sent back a detailed answer about the composition of
the stain. Its probably too long to repost here but the conclusion is that
"The stain is about as stable as dirt or wood, since it is composed
of polymerized phenols. The polymers were purified from humus, and
were named "humic acids". They contained approximately ten monomer
units in the chain."
He further states that the stain is probably more stable than the
gelatin of the emulsion.
If anyone wants the complete reply I will quote it to the list, I don't
think Mike would mind.
---- Richard Knoppow Los Angeles,Ca. dickburk@ix.netcom.com
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