[pure-silver] Re: More (Semi) Standing Around
- From: Tim Daneliuk <tundra@xxxxxxxxxxxxxx>
- To: "pure-silver@xxxxxxxxxxxxx" <pure-silver@xxxxxxxxxxxxx>
- Date: Mon, 8 Feb 2021 00:00:23 -0600
On 2/7/21 11:43 PM, `Richard Knoppow wrote:
By "etched" do you mean a relief image, visible by light reflected from
the surface of the negative? If so, its caused by differential hardening of
the emulsion. Pyro is known for this and also hydroquinone to a lesser
extent. This is the same hardening effect used to make matrices for dye
transfer printing and for some other processes. Kodachrome was known for
having a relief image but I don't know what caused it.
The differential hardening of pyro and other developers can result in an
edge effect due to the variation in the index of diffraction of the emulsion
at the borders of light and dark areas.
The same conditions that cause a stain image tend to cause the relief
image although I think the reaction products responsible for them are not the
same ones.
Indeed, that's what I'm referring to. Looking back at my older APX 100
negs done in PMK, there is some such slight effect, but the effect of
Pyrocat-HD on FP4+ is much more noticeable.
It is my understanding that the edge effect is caused by the exhaustion
of very dilute developer. Are you saying this only happens with Pyro-based
developers or might we see the same thing with, say, Rodinal or very dilute
HC-110?
Interesting you should mention Kodachrome. I do recall it having a very
visible and present relief image. I have never much been one to shoot
color, but the K25 product was among the best color film I ever saw (some
Polaroid films being the other). I actually just watched the Ed Harris
film "Kodachrome" again the other day. A lovely movie that features Dwayne's
Photo's last run of processing of Kodachrome. A Leica M figures in a number of
scenes.
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