Re: GENTLE BLEACH

From: Liam Lawless <liam.lawless@blueyonder.co.uk>
Subject: RE: GENTLE BLEACH
Date: Fri, 03 Jun 2005 00:15:56 +0100

> For reversal, you need a non-halogenising bleach that dissolves
> metallic silver WITHOUT altering silver halide, and I'm not aware of
> many suitable bleaches. Mike Ware suggested a bleach based on
> cerium nitrate, but I found it extrememly slow. It's also a great
> deal more expensive than permanganate and dichromate.

I can see cerium nitrate being a slow and expensive "bleach." Another
use for cerium (III) nitrate is to add it to the kettle when you are
making the emulsion formula you tried before. 0.3 mmol would be a good
starting point. (Did I tell you that? I probably never knew you have
cerium on hand!)

If the Ilford XP2-like film is available in the desired size and
suitable base, reversal processing like color reversal would be a bit
simpler because the film is first developed in b&w dev, fogged, and
then developed in color developer to form reversed dye image. Then the
whole silver image is bleached and fixed. (Or b&w reversal
"Kodachrome" could be made rather easily? By that I mean that the dye
coupler is introduced by the processing solution so that ordinary
films can be used for the purpose. It's just an idea.)

From: MARTINM <martinm@SoftHome.net>
Subject: Re: Chemist question for all of you who love to figure things out
Date: Fri, 03 Jun 2005 05:32:49 +0200

> Of course that's actually a fixing/bleaching solution ("BLIX")...

For the literal meaning I agree but I normally wouldn't use the term
for that bleach because bleach-flix is more commonly used for
dye-image system. Bleach-fix usually removes all silver image and
silver halides. On the other hand, the "gentle bleach" is a very lousy
fixer and a very slow bleach intended to make a small correction on
fixed material.

Also, I forgot to say that the "gentle bleach" solution doesn't keep
as long as most fixer solution because the pH is low enough to
decompose thiosulfate. It's best to mix fresh batches once every week
or every few weeks, whenever yellowish white precipitate is seen.

--
Ryuji Suzuki
"Well, believing is all right, just don't let the wrong people know
what it's all about." (Bob Dylan, Need a Woman, 1982)