[pure-silver] Re: Kodak Wash Aid Patent
- From: "Richard Knoppow" <dickburk@xxxxxxxxxxxxx>
- To: <pure-silver@xxxxxxxxxxxxx>
- Date: Wed, 18 Apr 2007 13:58:39 -0700
----- Original Message -----
From: "Lloyd Erlick" <lloyd@xxxxxxxxxxxx>
To: <pure-silver@xxxxxxxxxxxxx>
Sent: Wednesday, April 18, 2007 10:35 AM
Subject: [pure-silver] Re: Kodak Wash Aid Patent
At 06:41 PM 4/16/2007 , >Richard Knoppow wrote:
...
The patent states that the sequestering agent or
agents
are there to prevent precipitation the sulfite by calcium
or
magnesium salts in water or carried over alum hardner.
Citric acid is a good sequestering agent as is the EDTA.
Probably both are used in the commercial products because
one may be more effective for certain salts than the
other.
---
Richard Knoppow
Los Angeles, CA, USA
dickburk@xxxxxxxxxxxxx
====================
April 18, 2007, from Lloyd Erlick,
Sequestering agents are unnecessary if fixer is prepared
with distilled
water. (I haven't used hardener for decades ...).
I find the fixer Ansel Adams calls 'plain fixer' just
right. Two
ingredients (well, three if you count water). Cheap and
quick to mix. (If I
recall, the formula is in the appendix of The Print.)
regards,
--le
________________________________
Lloyd Erlick Portraits, Toronto.
website: www.heylloyd.com
telephone: 416-686-0326
email: portrait@xxxxxxxxxxxx
________________________________
--
Using distilled water will prevent calcium or magnesium
salts from the water used to mix the solution but will not
eliminate carried over alum hardener. Probably if a non
hardening fixing bath is used the sequestering agents are
not necessary. A simple mixture of Sodium Sulfite and Sodium
Bisulfite could be used. If there is no problem from the
sulfite being precipitated the sequestering agents are not
necessary.
Kodak usually designs its commercially packaged
chemistry to work under worst case conditions.
If no hardener is used a fixing bath needs only the hypo
and enough Sulfite to prevent its decomposition with time
and to take care of any carried over developer. Hardening
fixer needs tobe quite acid in order for the hardener to
work, the hypo works whether its acid or alkaline. The acid
in hardening fixer tends to decompose the hypo, hence the
relatively large amount of sulfite included. Most acid
fixers also have some means of buffering to maintain the pH
within the range that the hardener is effective despite
carried over developer.
---
Richard Knoppow
Los Angeles, CA, USA
dickburk@xxxxxxxxxxxxx
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