[pure-silver] Re: acrchival wash in cold water?
- From: "Richard Knoppow" <dickburk@xxxxxxxxxxxxx>
- To: <pure-silver@xxxxxxxxxxxxx>
- Date: Fri, 15 Apr 2011 13:36:05 -0700
----- 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?
That's good to know. I washed them for an hour in the
archival washer and then
left them in there overnight to leach out whatever else
was left. I'll give
them a little more wash before laying them on screens.
There's some definite
"B" prints in there so those will be good tests for the
toner.
Draining the water heater now and about to chase down an
installer. The
dimensions of the heater will be different than the old
one so better to have a
"pro" do it who can cut pipe etc where needed. We're also
in the midst of a
major electrical upgrade so yes, perfect timing! At least
Home Depot will give
me 12 months interest free on this purchase!
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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