[pure-silver] Re: print washer
- From: Richard Knoppow <dickburk@xxxxxxxxxxxxx>
- To: pure-silver@xxxxxxxxxxxxx
- Date: Tue, 18 May 2010 05:53:48 -0700 (GMT-07:00)
-----Original Message-----
>From: Myron Gochnauer <goch@xxxxxx>
>Sent: May 18, 2010 5:17 AM
>To: pure-silver@xxxxxxxxxxxxx
>Subject: [pure-silver] Re: print washer
>
>The Versalab was/is a great deal, but is no longer made, unfortunately. The
>tank itself is virtually indestructible. My 16x20 takes a huge amount of
>water, and thus requires a *very* sturdy sink! I never use it, since 16x20 is
>almost always a one-off, and the Kodak tray siphon + the occasional dump works
>well.
>
>Other fine 11x14 washers include the Darkroom Aids (stainless streel tank,
>plastic holder), and Red Village (simple but effective plexiglass tank with
>flexible nylon (?) rods to keep prints separated. (I *think* it was called Red
>Village.) Neither is made any longer, but both a easy to clean and would be
>worth keeping an eye out for.
>
>What else is/was out there? People have already mentioned the Zone VI and the
>Cascade. East Street Gallery was the original plexiglass type of archival
>washer, wasn't it? I have their 8x10 model. The dividers are so close together
>that you need print tongs to remove the prints.
>
>A slow one-hour wash, possibly with a couple complete dumps along the way,
>plus an over-night soak, produces excellent results with the HT-2 test. (no
>color or stain that I can see under strong light) Brighteners in the emulsion
>an unaffected by this wet-time.
>
>Myron
>
Heroic washing is not necessary and may damage the support. If sulfite
wash aid, such as Kodak Hypo Clearing Agent, is used double-weight paper will
wash out in half an hour. Overnight soaks will damage the support.
Washing of the emulsion is via a diffusion process. The hypo diffuses out
of the emulsion at a rate which depends on the ratio of the concentration of
hypo in the emulsion and in the wash water. It is exponential becoming slower
as it progresses. For fastest and most complete washing the water at the
surface of the emulsion should have the lowest possible concentration of hypo
in it.
The support washes out by a process which is only partially by diffusion.
The hypo is held by the paper fibers and must be removed by a frictional
process; that is why fiber paper washes out so much more slowly than RC paper
of film. A wash aid will accelerate the washing of the support but not as much
as it does the emulsion.
Paper and film _can_ be overwashed; T.H.James, of Kodak Research
Laboratories, discovered c.1961, that a very small residue of thiosulfate in
the emulsion stabilized the silver image giving it some protection against
oxidation by atmospheric peroxides and other polutants. The protection is
nowhere near as complete as that given by toning with a sulfide, selenium, or
gold toner but is significant. Similar results were found by the laboratory at
Fuji.
Some authors, David Vestal for example, used to recommend very long washes
and overnight soaks. Vestal changed his recommendations in light of the
discovery by James and Fuji.
In general, a sulfite wash aid will help to speed up washing and can help
remove some incompletely solubilized silver complexes left by partially
exhuasted fixer. It will conserve water. But, adequate washing can be obtained
without it although the wash times are something like five times longer. Wash
times need not be extended beyond Kodak's recommendations unless one encounters
problems with toning.
--
Richard Knoppow
dickburk@xxxxxxxxxxxxx
Los Angeles, CA, USA
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