From: ken watson (watsok@frii.com)
Date: 06/24/01-08:51:59 PM Z
Thanks for the explanations. IF the stain is proportional to silver I would
expect to see the stain in collodion as well. I was written off list that I
would not see much stain as collodion is not permeable to water. This may be
true once it dries but Liquids are used to sensitize and develop wet
collodion.
However, Richard mentions using lots of sulfite to make it non staining. I
assume this would be true for most highly acidic developers? If so this may
be the issue. I have used it in developer with Acetic and sulfuric acid.
Interestingly the developer turns light blue with acetic acid and a nice
bourbon color with sulfuric acid developer. Of course when I am done with
the developer it is very dark brown.
>From what I have read the pyro will not oxidize very rapidly in an acidic
solution. How much time do I have to use it before it starts to degrade? The
reason I ask is that I am adding Pyro to each "shot" of developer vs mixing
up a batch. Batching is more convenient.
..-----Original Message-----
..From: Richard Knoppow [mailto:dickburk@ix.netcom.com]
..Sent: Sunday, June 24, 2001 4:11 PM
..To: alt-photo-process-l@skyway.usask.ca
..Subject: RE: Pyro and staining
..
..
..At 10:55 PM 06/24/2001 +0100, you wrote:
..>Hi,
..>
..>Have a vague memory of having read somewhere that it is an
..oxidation product
..>of pyro that causes staining of gelatin. Since more oxidation
..takes place
..>in the heavily exposed areas, staining should be proportional to
..developed
..>silver densities.
..>
..>
..>
..>Liam
..>
..>
.. This is exactly correct. The oxidation product is related to humic acid,
..it is probably longer lasting than the silver.
.. Pyro can be made into a non-staining developer by using lots of sulfite.
..In fact, before M-H developers became the defacto standard most of the
..research into Pyro was directed to making it non-staining. These days the
..stain image is considered desirable. For printing materials which are blue
..sensitive the stain is opaque and adds linearly to the printing density.
..Pyro negatives are likely to look too light visually but print well.
.. The reaction which causes tanning of gelatin is related to the stain
..reaction, both take place together.
.. Presumably the stain reaction should take place in a collodion layer but
..I've never seen any experimental data so its only a guess.
..----
..Richard Knoppow
..Los Angeles,Ca.
..dickburk@ix.netcom.com
..
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