From: Christina Z. Anderson (firstname.lastname@example.org)
Date: 09/09/02-09:36:01 PM Z
Well, in searching through arcane photo books and with the help of some
on this list, I have figured out some stuff. Jimmy Peguet was the one who
made it all clear to me. Thanks, Jimmy, for taking the time to help me out.
Apparently there was an article in a French photography magazine about Denis
Brihat, one of the practitioners of these processes. In the article, which
Jimmy so kindly scanned and sent to me (luckily I read French) Brihat
mentions in there that Sudre was actually mistaken in calling his process
mordancage (English translation would be mordanting), because the process he
and Sudre use is more of what Brihat terms a "grignotage" or a nibbling of
the emulsion. That Sudre uses a formula more akin to bleach etch and NOT a
true mordanting formula is the case.
The differences between the two are that mordancage (actually really
bleach etch or gelatin relief) is a reverse relief process; dye mordanting
has no relief whatsoever. The gelatin surface remains level. Mordancage
uses hydrogen peroxide as the catalyst to dissolve the gelatin. Dye
mordanting just changes the gelatin in the print to one that accepts basic
dyes in direct proportion to the darks, usually with thiocyanate combined
with copper. The formulae seem similar except for the lack of hydrogen
peroxide in dye mordanting.
Still, bleach etch does not necessarily result in a negative gelatin
relief. It can run the gamut from a negative to part negative and positive,
because the highlights in a print do not dissolve, and when redeveloped,
remain positive. The darks, especially the blacks, do disappear and leave
paper base white where they once were. Or, you can not rub off the darks
completely and have wavy veils of gelatin that look like a polaroid emulsion
When gelatin relief/bleach etch/etc came into being (as early as 1897)
it was a method of making a film negative into a positive. There were ways
to color this, in an attempt to create color film. This is a vast
condensation of the literature on the subject with all kinds of differing
formulae which I am still trying to wade thru and then test, but I'm
comfortable with the answers to my original questions on this list of a
while ago that had remained unanswered.
Nate Apkon is currently testing out dye mordanting, and it will be
interesting if this process still has visual interest to us today. I know
mordancage does for me.
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