Liam Lawless (lawless@vignette.freeserve.co.uk)
Wed, 27 Jan 1999 00:03:37 +0000
Hi Steve,
My Darkroom Cookbook lists Formula #123, Kodak Amidol Redeveloper, under the
heading "Miscellaneous" near the end of the book - is this the one you mean?
If so, it says to use with S-6 Stain Remover, Formula #124 and gives full
instructions over the page. Anchell says not very much about why we might
want to bleach and redevelop, but I imagine these formulae are for removing
various kinds of staining rather than modifying contrast, density, etc., and
while I haven't actually used any of them for that purpose, old texts often
say stain removing methods are not always effective.
The idea of this kind of remedy is that stains and fading of prints are
usually caused by the silver changing to silver sulphide or silver oxide,
but they can be redeveloped after converting to e.g. silver chloride (which
also, of course, happens to the unfaded/unstained parts of the image).
Repair is not possible when the silver has turned to silver sulphate - which
it does under certain circumstances that I cannot now remember - since this
is a water-soluble compound.
A powerful bleach is needed because ferricyanide-bromide, for example, does
not affect silver sulphide, but I would guess that almost any print
developer would accomplish much the same thing, though the image colour
might vary. Film developers are not used after bleaching - even on films -
because many have a high sulphite content that attacks the bleached silver
before the developing agents can restore it to silver.
If you just want to play and explore the effect of different bleaches and
developers (developers at high dilution can produce interesting brown to red
tones on some papers), almost any bleach will do, and the simplest is
probably the ferricyanide-bromide that comes with commercial sepia toners
(though they sometimes also contain other additives). However, a bleach
that changes silver into silver chloride (such as copper sulphhate +
sulphuric acid + sod. chloride, or Kodak S-6 stain remover, as quoted by
Anchell) is probably better for this purpose.
For bleaching in order to harmonise negatives, I find ordinary
ferricyanide-bromide quite satisfactory. Iodide bleaches (e.g. iodine
dissolved in pot. iodide solution, or in alcohol) have some interesting
properties that are useful in certain toning applications, but toning or
redeveloping after bleaching to silver iodide can be incredibly slow.
There's something interesting about Kodak S-6 Stain Remover and Sandy's
bleach. I'll be posting a message to him about this.
Hope this helps,
Liam
-----Original Message-----
From: Steve Shapiro <sgshiya@redshift.com>
To: alt-photo-process-l@sask.usask.ca <alt-photo-process-l@sask.usask.ca>
Date: 26 January 1999 02:35
Subject: Re: Pyro redevelopment
>Steve Anchell's "Darkroom Cookbook" shows a formula for redevelopment,
>Amidol Redevelopment formula; and I wanted to know if a bleach
>composite/formula is necessary. What is the simplest bleach formula for
>redevelopment, anybody know?
>
>S. Shapiro
>sgshiya@redshift.com
>-----Original Message-----
>From: Sil Horwitz <silh@iag.net>
>To: alt-photo-process-l@skyway.usask.ca
><alt-photo-process-l@skyway.usask.ca>
>Date: Sunday, January 24, 1999 3:32 PM
>Subject: Re: Pyro redevelopment
>
>
>>At 10:11 AM 1999/01/24 -0400, Sandy King wrote:
>>
>>>>This still doesn't explain Sandy's results. As a matter of interest,
>Sandy,
>>>>why is there bromide in your bleach?
>>>
>>>Quite frankly I don't know exactly what the bromide does but it is
>>>recommended in the formula of several super proportional reducers that I
>>>have on hand. I am going to assume that its primary function is to
>restrain
>>>the heavier silver deposits and reduce overall density, but this is only
>>>speculation.
>>
>>In most bleaches, there is an oxidizer to produce a reactive silver ion,
>>and a receptor (like bromide) to combine with the ion immediately to form
>>silver halide (silver bromide if there are bromide ions present). Silver
>>halides, of course, can then either be dissolved in fixer, or made to
>>further react with another substance (as is done in toning).
>>
>>Sil Horwitz, FPSA
>>Technical Editor, PSA Journal
>>silh@iag.net
>>Visit http://www.psa-photo.org/
>>Personal page: http://www.iag.net/~silh/
>>
>
>
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