[pure-silver] Re: acrchival wash in cold water?
- From: Eric Nelson <emanmb@xxxxxxxxx>
- To: pure-silver@xxxxxxxxxxxxx
- Date: Fri, 15 Apr 2011 15:38:24 -0700 (PDT)
I was mostly interested in the optimum water heater specs but have found one,
not at home depot, and supposedly much better brand than they sell. Bradford
White is the brand in case anyone finds themselves in the same boat.
The 'instant' water system has it's downsides plus added plumbing expenses.
We've been getting clobbered by the electricians, plumbers and various other
trades people coming through here. Our building is a 2 flat and we don't see
ourselves living here forever, so this unit will be more than adequate for our
future tenants.
RE: Washing....I also remember there being speculation re:the OBA's in the
paper
being washed away in a long wash. I checked that today and these prints still
glow nicely under UV. Whether as brightly as before is a valid question.
Richard your point is well taken and I always think of you & the too much/too
long washing issue, and these concerned me. But I hated the idea of pulling
"partially" washed prints out and drying them as, in my mind, I believed that
if
done that way, the fixer left in the prints would permanently adhere to the
paper. Not to mention the probable contamination of the drying screens. My
belief was unsubstantiated by fact but afaik not discounted either! =)
A re-wash, once hot water is restored tomorrow, was a possibility, but I just
wanted to make sure I didn't carry over fix to the screens and have it stuck in
the prints forever as well.
I kind of alternated between diffusion and friction with some washes since
yesterday giving the water time to warm up in the pipes inside before the 45°
water got to the washer.
Anywho, fingers crossed, they are in the dryer and once the heater is installed
tomorrow I can finish the job.
________________________________
From: Richard Knoppow <dickburk@xxxxxxxxxxxxx>
To: pure-silver@xxxxxxxxxxxxx
Sent: Fri, April 15, 2011 3:36:05 PM
Subject: [pure-silver] Re: acrchival wash in cold water?
----- Original Message ----- From: "Eric Nelson" <emanmb@xxxxxxxxx>
To: <pure-silver@xxxxxxxxxxxxx>
Sent: Friday, April 15, 2011 7:39 AM
Subject: [pure-silver] Re: acrchival wash in cold water?
Since I rent I have no idea where to buy a water heater.
Overnight soaks are not a good idea and I intended to add that to my post.
Such soaks were suggested by David Vestal and possibly even Ansel Adams in the
past. Vestal retracted his advice in his later books.
There are a couple of problems with long soaks: they can damage the paper
support; while the paper used for photographic paper has very good wet strength
it will eventually begin to disintegrate, also, the emulsion and barytal layers
can begin to delaminate.
Further, since washing is partly a diffusion process and for the paper
support, partly a frictional process, the water at the surfaces must be renewed
frequently or the hypo will reach a sort of equilibrium and the further
diffusion be slowed to a stop.
In the emulsion, and in the baryta substrate, the hypo and reaction
products
wash out mainly by diffusion but, according to Ilford research, the hypo in the
paper support is partly held by frictional forces to the fiberous structure.
That is the main reason that "fiber" or untreated paper takes so long to wash
out. In the emulsion and baryta substrate the hypo and reaction products are
held by chemical binding of two varieties, both of which are broken by the use
of a buffered sulfite wash aid such as Kodak Hypo Clearing Agent, and the
evidently identical Iford product. The two kinds of bonds are: a bond due to
the
electrical charges in the gelatin of both emulsion and substrate; and, a
chemical bond due to the use of white alum hardener. This last is not present
when a non-hardening fixing bath is used or when chrome alum is used as the
hardener (never for prints because it stains). Both bonds are pH dependant. By
increasing the pH to neutral the "mordanting" bond of white alum is eliminated
without loosing the hardening effect. Greater pH will also break the bond but
will also eliminate the hardening. Since photographic gelatin has an
isoelectric
pH slightly on the acid side of neutral the internal charges tend to attract
ions with even lower pH, this tends to hold the hypo and any reaction products
to the gelatin when an acid fixer is used. By increasing the pH to neutral the
charges are changed so that the gelatin is slightly more alkaline than the hypo
so that the charges repel and facilitate washing.
Sodium sulifte, and other sulfites, have a further effect on washing; they
act to displace thiosulfate ions through a process known as ion exchange. This
active displacement takes place even when a non-hardening or non-acid fixer is
used, much accelerating washing and making the wash less sensitive to
temperature. When a wash aid such as KHCA is used the wash time for film is
reduced to about 1/6th the time needed for film treated in a hardening, acid
fixing bath and for fiber paper about the same if you consider one hour a
sufficient normal time for double weight paper.
Overwashing.
About 1961 T.H.James, of Kodak Research Laboratories, discovered that a
very small residue of thiosufate in the emulsion would _stabilize_ the image
where it was exposed to oxidizing agents such as peroxides in the air. His
discovery meant that the sort of very long washes and soakes recommended at the
time resulted in _less_ not morestable images. This was such heresy that he was
reluctant to publish the results until a researcher from Fuji's laboratory
published similar results. The result of this was that Kodak completely revised
their recommendations for residual thiosulfate in archival materials and with
that their washing recommendations.
There are no very definite quantities given for the desired amount of
thiosulfate remaining but Kodak's washing recommendations since the 1960's
reflect it. The recommendations for washing after using KHCA also take this
into
consideration.
The protection provided by the thiosulfate residue is minimal, it does not
take the place of toning but James and others found that even when dilute
selenium toner was used the resistance of images to oxidation was greater when
the residual thiosulfate was present.
Highly diluted (1:19) Kodak Rapid Selenium Toner is no longer recommended
as
a routine method of protecting iamges because it was discovered about twenty
years ago that it no longer seemed to work. This was the result of research by
the Image Permanence Institute into why microfilm at a large archive were
showing signs of image degradation despite having been processed according to
the accepted recommendations for permanence. There was never any definite
answer
as to why the treatment had stopped working; Kodak stated that neither the
formula or method of production of KRST had changed. There was speculation that
some raw material used in the original had some impurity that resulted in the
superior protection but that remains only speculation, the fact is that KRST,
in
high dilutions tones different size silver crystals at different rates, the
result being that low density areas are not protected.
KRST was popular because it was cheap, easy to use, and did not
significantly change the density or structure of the silver image, both of
which
are vital to microfilm use.
KRST will provide full protection if used in stronger dilutions, Dr.
Douglas
Nishimura, the principal researcher at IPI, recommends not less greater than
1:9
and for not less than 3 minutes @ 68F. IPI now recommends a polysulfide toner
like Kodak Brown Toner for routine use on microfilm. The old standard Gold
toner
is still considered the standard but is quite expensive.
--
Richard Knoppow
Los Angeles, CA, USA
dickburk@xxxxxxxxxxxxx
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