[pure-silver] Re: PMK
- From: "Richard Knoppow" <dickburk@xxxxxxxxxxxxx>
- To: <pure-silver@xxxxxxxxxxxxx>
- Date: Fri, 28 Apr 2006 09:57:43 -0700
----- Original Message -----
From: "Koch, Gerald" <gkoch02@xxxxxxxxxx>
To: <pure-silver@xxxxxxxxxxxxx>
Sent: Friday, April 28, 2006 7:27 AM
Subject: [pure-silver] Re: PMK
Fixer is heavier than water and will tend to sink unless the
wash water
is kept moving.
Jerry
Oh dear, this is a very old myth. Fixer diffuses out of
the emulsion and continues to diffuse into the surrounding
water. If the water is still the fixer will eventually form
a cloud of of diminishing concentration until it reaches
equalibrium in the whole volume. The concentrated hypo at
the suface might begin a convection current but, because it
goes into solution with the water, will never stratify like
oil. The idea of keeping the water agitated is to prevent
the water at the emulsion surface from reaching equalibrium
with the emulsion thus stoping the diffusion. The washing
takes place in a very thin layer right at the emulsion. If a
washer is made to provide a constant flow of fresh water at
the surface it will be very efficient and also conservative
of water. An ideal washer would have minimum volume and
maximum flow rate.
The same is true of fiber prints except the hypo diffuses
out of the support as well as the emulsion. Paper washes out
slowly because the hypo is held in the fiber structure by
frictional forces and is released slowly. A sulfite wash aid
will help wash it out but is far less effective for the
paper base than for the emulsion.
FWIW, Kodak research showed that if its desirable to
remove all hypo from the paper base an oxidizing hypo
eliminator like the old Kodak HE-1 is necessary. Since HE-1
will not remove silver complexes from the emulsion its
necessary to treat the print with Kodak Hypo Clearing Agent
first, followed by a wash, followed by HE-1 with potassium
bromide added (1.0 gram / liter of HE-1), followed by a
wash. At one time Kodak recommended this procedure. The use
of a sulfite bath or KHCA before the HE-1 also eliminates
occasional stainging in the HE-1. HE-1 should NEVER be used
on film. It purpose above is only to remove hypo from the
paper support of fiber prints, probably not necessary.
Note that a print treated this way will be very
vulnerable to oxidation by atmospheric polutants unless
toned in a sulfiding or gold toner.
A note to Ruyji, I am really including the HE-1 stuff for
historical and academic interest, I don't actually use this
procedure (although I've tried it) and am not recommending
it.
---
Richard Knoppow
Los Angeles, CA, USA
dickburk@xxxxxxxxxxxxx
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