[pure-silver] Re: Kodak Wash Aid Patent
- From: "Richard Knoppow" <dickburk@xxxxxxxxxxxxx>
- To: <pure-silver@xxxxxxxxxxxxx>
- Date: Tue, 10 Apr 2007 20:52:05 -0700
----- Original Message -----
From: "BOB KISS" <bobkiss@xxxxxxxxxxxxx>
To: <pure-silver@xxxxxxxxxxxxx>
Sent: Tuesday, April 10, 2007 7:19 PM
Subject: [pure-silver] Re: Kodak Wash Aid Patent
DEAR RICHARD,
Wouldn't the MSDS tell you exactly what is/was in the
marketed
product though it wouldn't indicate quantities? If there
is/was a citrate
in the actual product, wouldn't it appear in the MSDS?
CHEERS!
BOB
I made an error in saying citrate, actually, its citric
acid, listed with other sequestering agents. Citric acid is
not included in any of the example formulas in the patent
but is listed in the MSDS. According to the patent the
purpose of the EDTA Tetrasodium Salt and Citric Acid is to
prevent precipitation of the sulfite by calcium salts in the
water and carried over aluminum salts from the fixing bath.
In general, MSDS do not always list all of the
ingredients of a product. If something is considered
non-hazardous, or is present in very small amounts, it may
be omitted. MSDS for various countries may differ in what is
listed. Australian MSDS, for instance, often list stuff not
found in US MSDS. Another problem is that MSDS list
ingredients in order of approximate percentages. This is
quite inexact and often difficult to translate to actual
amounts where there may be filler (in the case of poweder
for instance) of unknown amount. The EDTA and Citric acid in
KHCA are listed as being present in amounts from 1 to 5
percent, that is a pretty large range. The patent gives an
actual formula. Since the MSDS indicates the the EDTA and
Citric acid are present in approximate equal quantities one
can guess at the amount of Citric acid. However, there may
be a some variation in the proportion of Sulfite to
Metabisulfite. The target pH of the wash aid is 7.0 and
those more expert in chemistry than I can probably calculate
the pH.
In any case, the patent re-inforces some statements
made in the research paper published by Henn, King, and
Crabtree describing the solution. For instance, it makes it
clear that the sulfite wash aid will help remove silver
complexes as well as thiosulfate, something that neither an
alkali bath or the old Kodak Hypo Eliminator will do. It
also discusses the problem of increased vulnerability of
well washed prints to oxidation by peroxides, etc., and the
need for toning for stability. A combination of wash aid
with Selenium is described. It has been found more recently
that combining KHCA with Kodak Rapid Selenium Toner, a
standard treatmen for years, is not completely effective on
microfilm. The patent describes a more direct method of
including Selenium in the wash aid. I have no idea if this
arrangement has ever been tested or whether it has the same
faults as the weak dilution of KHCA. The patent makes
interesting reading and is not too difficult from the
"patentese" standpoint. Its only 3 pages so does not take
long to download.
---
Richard Knoppow
Los Angeles, CA, USA
dickburk@xxxxxxxxxxxxx
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