[pure-silver] Re: Fixing time for fiber
- From: "Richard Knoppow" <dickburk@xxxxxxxxxxxxx>
- To: <pure-silver@xxxxxxxxxxxxx>
- Date: Thu, 9 Aug 2007 23:39:00 -0700
----- Original Message -----
From: "Eric Nelson" <emanmb@xxxxxxxxx>
To: <pure-silver@xxxxxxxxxxxxx>
Sent: Thursday, August 09, 2007 9:06 PM
Subject: [pure-silver] Re: Fixing time for fiber
Eric,
Are you talking about stop bath that is too weak to
acidify the print, thereby shortening the life or
activity of the fixer? Or just not draining the print
long enough before it hits the stop?
Eric
--- EJ Neilsen <ej@xxxxxxxxxxxxxxxxxxxxxxxxxx> wrote:
Stop bath will immediately stop development and
inactivate the developer. A 30 second soak will also wash
out much of the developer. Standard acid hardening fixing
baths are designed to withstand a considerable amount of
carried over developer since most of them were designed in
the 1930s when many photographers did not stop baths. A
standard fixing bath like Kodak F-5 or Kodak packaged fixer,
is well buffered using and also contains an excess of Sodium
Sulfite. The Sulfite serves two purposes: first, it prevents
the decomposition of the Thiosulfate by the acid, and
secondly, it prevents staining from carried over developer.
If the fixing bath is neutral or alkaline its possible
for the developer to reactivate in the fixing bath. If there
is enough sulfite it may not cause the usual yellow stain
but can produce dichroic fog from deposits of metallic
silver on the surface of the print. This is caused by the
developer reacting with dissolved halide complexes in the
fixing bath. A fixer, even if alkaline, would have to be
close to exhaustion for this to happen, unless it was made
without sulfite or with very little sulfite.
From the description of the original problem I do not
think it was caused by developer stain. That usually shows
up very quickly, sometimes immediately after fixing. More
likely it was caused by sulfiding of the image from somthing
in the atmosphere. Untoned prints are quite vulnerable to
this and to oxidizing. Oxidizing usually is manifested as
silvering out, that is, the production of a black stain or
even a mirror-like deposit over high density areas.
Sulfiding causes the image to turn brown or yellow.
Sometimes the sulfide migrates but usually not.
There is a limited amount of protection of the image if a
very small amount of Thiosulfate is allowed to remain in the
emulsion. The amount is very small, a larger amount causing
the usual staining. However, the current Kodak and other
recommendations for washing and for the use of a wash aid
reflect this fact. If a print or film is washed to the point
where there is no thiosulfatge whatever in it toning becomes
absolutely necessary to protect the image.
Display prints should always be toned to prevent attack
by airborne polutants. Effective protective toners include
all sulfiding toners, Selenium when it is carried out far
enough, and Gold toners. Gold is very effective and results
in a cold or neutral image for many papers but is too
expensive to be used routinely.
Some sulfiding toners can not be used for partial toning
because they do not tone the image uniformly. Full toning
with any of them results in very permanent images but they
will be the usual Sepia color.
Stabilizing agents like Agfa Sistan and Fuji Ag-Guard are
effective but not as much as a toner. If its absolutely
necessary that the image color and density not be changed
one of these may be useful. While not as effective as a
toner they will nonetheless give significant protection
where a print must be displayed or stored under adverse
conditions.
---
Richard Knoppow
Los Angeles, CA, USA
dickburk@xxxxxxxxxxxxx
=============================================================================================================
To unsubscribe from this list, go to www.freelists.org and logon to your
account (the same e-mail address and password you set-up when you subscribed,)
and unsubscribe from there.
Other related posts:
