From: Richard Knoppow (dickburk@ix.netcom.com)
Date: 03/04/03-05:50:52 PM Z
----- Original Message -----
From: "Liam Lawless" <liam.lawless@blueyonder.co.uk>
To: <alt-photo-process-l@sask.usask.ca>
Sent: Tuesday, March 04, 2003 2:26 PM
Subject: RE: C-41 in b&w chemistry
> Keith,
>
> The C-41 emulsion contains three layers of silver halides
and colour
> couplers. Oxidation by-products of silver development
combine with the
> couplers to form the C, M and Y dyes, after which the
silver (thinner than
> in B&W film) is no longer needed and is bleach-fixed away
to leave just the
> three dye images. Or something like that.
>
> With a straight b&w developer, the coloured dyes do not
form and you end up
> with just a thinnish silver image. Plus, I think I read
somewhere, the
> unused couplers contained in oily globules, which I
believe can be removed
> (with alcohol, perhaps?)
>
>
> Liam
> -----Original Message-----
> From: Keith Gerling [mailto:keithgerling@att.net]
> Sent: 04 March 2003 19:06
> To: alt-photo-process-l@sask.usask.ca
> Subject: OT: C-41 in b&w chemistry
>
>
> Can anyone here explain what would happen if C-41 film
happened to be
> processed in chemistry intended for black and white film?
>
> (no, I didn't actually DO this. Just curious)
>
> Thanks!
>
The film must be fixed after development. The couplers
used in two layers of most color films are themselves
colored. This forms a color correction mask when developed
normally, but leaves an orange overall color when deloped in
B&W developer.
Color developers are derivatives of
para-phenylenediamine. As you state the reaction products of
the developer further react with the couplers to produce
dyes. Other types of developers may or may not react with
the couplers.
Two methods have historically been used for anchoring the
color couplers in the emulsion, so that they don't wander
from layer to layer. The first method was devised by Agfa in
the mid 1930's. This works by attaching the coupler
molecules to long chain molecules, which are too large to
move through the gelatin. Kodak came up with another method,
c.1940, encapsulating the couplers in a resin. Developing
chemicals can penetrate the resin but the coupler and dye
can not. Developers for this process often conatin alcohol
to help the developer penetrate the resin. These films or
papers tend to look "pearly" after processing until
completely dry. I am not quite sure which system has
survived.
Kodak has a sheet describing development of color films as
B&W hiding somewhere on its web site. I believe they
recommend bleaching out the couplers using fresh ammonium
thiosulfate fixer (Rapid fixer) with about 15 grams/liter of
citric acid added.
--- Richard Knoppow Los Angeles, CA, USA dickburk@ix.netcom.com
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