[pure-silver] Re: Hardening fixer for film
- From: "Richard Knoppow" <dickburk@xxxxxxxxxxxxx>
- To: <pure-silver@xxxxxxxxxxxxx>
- Date: Wed, 18 Apr 2007 00:27:57 -0700
----- Original Message -----
From: "Laurence Cuffe" <cuffe@xxxxxxx>
To: <pure-silver@xxxxxxxxxxxxx>
Sent: Tuesday, April 17, 2007 7:18 PM
Subject: [pure-silver] Re: Hardening fixer for film
On Tuesday, April 17, 2007, at 05:00AM, "Snoopy"
<snoopy@xxxxxxxxxx> wrote:
At 18:31 16.04.2007, you wrote:
It would be interesting to know when IPI
tested Sistan. A few years ago I had
considerable correspoindence with Dr. Douglas
Nishimura of IPI about several permanence
issues. He mentioned that Sistan had never been
given a formal test. I have to go by memory but
I think he said that they started to test the stuff and
Agfa withdrew it.
Dear Richard,
this might have something to do with the fact,
that there are two Sistans: the "old" Sistan -
this is the one I used in my long-bygone youth
and this is the one where I was told to use it in the
AGEPON.
Then came (I don´t know when) "Sistan New". It
might well be that this was introduced because a
law disallowed a chemical component or marketing reasons or
somesuch.
My memory of this when it came out was that Sistan new was a
more dilute version of sistan with the same active
chemistry. If sistan is used at too high a concentration it
can cause problems and apparently photographers are not
immune to the idea that you cant have too much of a good
thing.
Prints should not be washed after the final bath. Sistan
leaves a small amount of potassium thiocyanate lying around
on the print. If oxidized silver compounds form, this reacts
with them to form silver thiocyanate which precipitates back
onto the silver particle being attacked. This compound is
transparent and resists oxidation.
This is from Ctein's book post exposure, and seems eminently
plausible. In his testing he found it effective in
preventing silvering out on treated areas of RC prints which
were displayed in a lighted area. More details are on
p161-162 of his book.
I hope this helps,
Larry Cuffe
So it might be that they withdrew the old Sistan
from the test and then had the new stuff tested.
Because the data sheet where the info is from pertains to
"Sistan New".
Actually if you don´t mind me saying so, I don´t
really care much if its "formally" tested. From
what people say here (and I trust them) it does
make a positive difference. Since all the
information here is for prints and I use it on
film I reckon I am "on my own" anyhow ??
Love,
Snoopy
I am not snipping because I want to respond to some
things in both posts.
First of all, I am NOT a photochemist or a chemist of any
sort. I know what I have picked up from those who are. Ryuji
Suzuki is one and there have been others. I am, however,
something of a skeptic due to early training in the sciences
and, perhaps, because my dad was an attorney and taught me
to be careful of what I accepted as fact.
I was sure that IPI never formally tested Sistan, this
turns out to be correct. They evidently tried some very
early testing which did not turn out well. In any case Agfa
decided against testing. Sistan may very well work as
advertised but there has never been any independent research
published. I am somewhat skeptical of Ctein's work although
he may well have done proper accelerated aging testing. I
was told by Dr. Nishimura that partial testing of Fuji
Ag-Guard also did not turn out well but Fuji subsequently
published a proper research report (sorry, I do not have the
citation) which showed that Ag-Guard was effective in
preventing attack by peroxides in the atmosphere but that it
was not as effective as proper sulfide or Gold toning. I
suspect the same may be true of Sistan. Ctein's theory of
how Sistan works sounds OK but again, I am not a chemist and
I would like to hear a chemists reaction to it.
The IPI testing of various toners for microfilm is
reported in a quite large report which describes the methods
and experimental design in detail and reports raw as well as
reduced data so that the reader has a chance to spot any
errors (or blunders) that may have been made. This is a
standard requirement for the reporting of scientific
experiments. Where they are absent I think it is wise to
remain skeptical.
I also believe that the main difference between the
original and the "neu" Sistan is mostly in concentration. In
too large an amount the Thiocyanate in Sistan could attack
the image in much the same way as Thiosulfate.
There is a curious thing that should be mentioned here.
Up to the 1960's it was thought that for archival life (100
years or more) photographic materials had to be washed until
there was virtually no Thiosulfate left. About 1961 Thomas
H. James, of Kodak Research Laboratories, discovered that a
small residue of Thiosulfate in the emulsion actually
provided protection against oxidation. The theory is that
the Thiosulfate causes a very small amount of silver at the
surface of each grain to become Silver Sulfide, which is a
very stable substance. The problem is that there is no very
good way of determining the optimum amount but the discovery
caused an immediate change in the recommended washing
practices. The discovery was such heresy that James did not
publish at once. However, someone at Fuji's research
laboratory made a similar discovery and did publish causing
James to do likewise. Kodak's current recommendations for
after treatment and washing reflect this discovery. Washing
for longer or excessive treatment in a wash aid actually
reduces the stability. I believe based on what I have been
told that the Thiocyanate in Sistan and whatever is in
Ag-Guard are intended to serve a similar purpose but in a
controlled amount.
The protection afforded by the residual Thiosulfate is
far below that obtained by toning in a sulfiding toner, or
in a Gold toner or even in Selenium toner provided that
toning in Selenium is carried out far enough to overcome its
tendency to tone fine grained particles of silver before the
coarser ones. While Kodak Brown Toner and similar Liver of
Sulfur toners, including the old Agfa Viradon, tone all
particle sizes equally some other sulfiding toners do not
and have the same problem as KRST. Notable are the Hypo-Alum
type toners which also tend to tone the highlights before
the shadows. Bleach and redevelop ("indirect") toners will
provide good protection _provided_ the bleach step is
carried out completely so that no metallic silver remains in
the emulsion. Also, the resultant toned prints probably
should be re-fixed to remove any metallic silver which may
remain. The same is true of the Hypo-Alum type toners. KBT
and other Liver of Sulfur toners do not need refixing to
insure permanence.
---
Richard Knoppow
Los Angeles, CA, USA
dickburk@xxxxxxxxxxxxx
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