[pure-silver] Re: Bleach
- From: "Richard Knoppow" <dickburk@xxxxxxxxxxxxx>
- To: <pure-silver@xxxxxxxxxxxxx>
- Date: Fri, 18 Dec 2009 01:24:47 -0800
----- Original Message -----
From: "Tim Rudman" <tim@xxxxxxxxxxxxx>
To: <pure-silver@xxxxxxxxxxxxx>
Sent: Thursday, December 17, 2009 10:45 AM
Subject: [pure-silver] Re: Bleach
Hello Alan,
The bleach used in sepia toning is potassium ferricyanide
(not as awful as
it sounds!) with an added halide or halides to facilitate
redevelopment in
the toner. The halide is commonly potassium bromide.
For bleaching local areas of a print potassium
ferricyanide is usually used
without the bromide and is either mixed with or followed
by fixer.
If the spot is black you will be more successful with an
iodine bleach,
which bleaches down to white whereas PF will leave a pale
yellow brown.
If the spot is grey and needs lightening PF is excellent.
If black it is
easier to take to white with iodine and spot in
afterwards.
Tim
Note that the iodine bleach needs to be followed by
fixing as well. Even though Farmer's Reducer which is the
potassium fericyanide bleach, contains fixer the finished
print or negative should be refixed in regular fixer to
insure no silver halide is left. If there is any it will
eventually cause staining. Plain iodine as available from
the drugstore works fine although you may want to dilute it
with water or alcohol. It works quite rapidly.
Household bleach, used full strength, will remove the
emulsion completely. It has little, if any, use in
photography other than as a cleaner.
--
Richard Knoppow
Los Angeles, CA, USA
dickburk@xxxxxxxxxxxxx
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