[pure-silver] Re: Fixing time for fiber
- From: "Richard Knoppow" <dickburk@xxxxxxxxxxxxx>
- To: <pure-silver@xxxxxxxxxxxxx>
- Date: Thu, 9 Aug 2007 10:55:44 -0700
----- Original Message -----
From: "Eric Nelson" <emanmb@xxxxxxxxx>
To: <pure-silver@xxxxxxxxxxxxx>
Sent: Thursday, August 09, 2007 8:47 AM
Subject: [pure-silver] Fixing time for fiber
I'm preparing an HT-2 solution and the ST-1 solution
to diagnose a couple prints that have turned on me.
I use a double kodak rapid fixer bath and test them
till they are exhausted and then toss them, rotating
the fixer #2 into the #1 position and making a new #2
bath. I fix for a total of 5 minutes and then go to a
water bath OR directly to the washer where they may
wash for 15-30 mins. before they go to a still water
bath to wait for hypo clearing when I finish the
printing session. I wash for over an hour in a
vertical archival washer after hypo clearing. I've
never had any problems toning afterwards.
The prints in question have turned yellowish brown
ONLY in the image area which, without testing, says to
me that they didn't get enough fixing. I have always
been leary of fixing for too long with fiber, but that
may have come back to bite me you-know-where.
So, speaking to Richard's comment of going longer in
the fixer depending on the number of prints that have
gone through the solution, I'd like to work with a
fixing time that I can depend on without having to get
all empirical and test these dang prints all the time.
Is there a dependable time for that? Obviously 5
minutes total time in partially used fixers needs to
be longer but I don't want to over-fix either.
Any suggestions?
As a side note, in speaking with Kodak professional I
found the person I spoke to lacking in knowledge in
regard to the testing solutions for silver and hypo.
I wonder, since they no longer make paper, if they are
phasing out support/knowledge of paper related issues.
The information can be found elsewhere via the web of
course, but isn't too helpful for a novice or the
uninitiated who may not know what to look for.
Eric
Yellowing in the image area is unusual for a toned print,
were these toned? Clear borders suggests the fixing was
complete but it can still be tested using the sulfide test
solution. Any remaining halide or fixer reaction products
should still stain. If the pictures were toned in Selenium
its like the toner would have stained the highlights. A 1:9
dilution of KRST was recommended by Kodak as an alternative
to the Sulfide test but it works only on washed prints, the
stain may not appear if there is a lot of hypo left in the
print.
Its possible that there were fixer reaction products
bound to the image silver. Usually a sulfite wash aid will
remove these but they could cause imagewise staining.
Lack of adequate washing will also cause staining but its
usually not confined to the image.
It is also possible the images were stained by a
sulfiding polutant in the air. Oxidation is a more common
type of damage these days but sulfiding is still possible.
KRST in weak solutions, i.e., 1:20, does not provide
adequate protection to low density areas of the print and
can leave them vulnerable to both sulfiding and oxidation.
There are many sources of peroxides and sulfides such as
fumes from fresh paint, unvented gas heaters, etc.
Kodak's instructions for testing two bath fixers using
their Iodide fixing bath test are somewhat confusing. The
test should be more sensitive for the second bath and a
lower concentration is indicated for it, which should
_lower_ the sensitivity. In any case, I think a better test
is to fix out some wetted but otherwise unprocessed paper
and test it with the sulfide test. This should show if
fixing is complete.
The first bath of a two bath system can be run for longer
than if it were a single bath. According to Ilford tests the
capacity of a single bath to provide complete fixing is
extremely limited, only about 10 8x10 sheets per _gallon_.
The use of a two bath system, especially if followed by a
sulfite wash aid, multiplies this by four to ten times.
The reason the sulfite bath extends the fixer capacity is
that is makes soluble some fixer complexes which otherwise
remain bound to the gelatin.
Fixing is a stepwise process in which the undeveloped
halide is made increasingly soluble in several steps. To
make it completely soluble about three ions of Thiosulfate
are needed for each silver halide ion. If there are not
enough Thiosufate ions available the halide is never made
completely soluble. The remaining complexes will eventually
attack the image causing sulfiding and staining.
After treatment in the sulfite bath washing is
comparitively rapid but the hypo in fiber paper is retained
by the Baryta layer and the fibers of the paper. In both it
is harder to wash out than from the emulsion. Printing paper
emulsions are relatively thin and, by themselves, wash out
very rapidly. As proof note that RC paper will wash out in
about four minutes even when acid, hardening fixer is used
and no wash aid is used. It is the Baryta layer and,
especially, the paper support, which require such long wash
times for fiber.
Fixing time should be determined by tests using the
Sulfide test solution. Dave Valvo has pointed out that in
fiber base paper some halide can get into the Baryta layer
were it is relatively difficult to fix out. This is one
reason longer fixing times are recommended for fiber paper
than for RC. Also, emulsions vary. For instance, the Ilford
Archival method requires very short fixing times in strong
Ammonium Thiosulfate fixer (rapid fixer at film strength). I
works on the Ilford papers it is recommended for but not on
many other papers. While the Ilford papers will fix out in
30 seconds to a minute some Kodak papers require two minutes
or more for to completely fix. Where this is the case the
fixing and wash aid treatment and washing should follow
Kodak recommendations.
In Sodium Thiosulfate fixer the emulsion of most papers
will fix out in about the same time recommended for RC:
about 2 minutes, but, because some emulsions may require
longer times, and because of the Baryta layer, longer times
may be necessary. Again, test using the Sulfide test. I
would process a scrap of undeveloped but otherwise processed
(stop bath etc.) along with the prints for testing purposes.
The reason for wetting the paper before testing the
fixer is because the fixing rate is different for wet and
dry emulsions. This was discovered by Kodak labs in the
1940s when they revised the findings of earlier research on
the effect of the concentration of Thiosulfate on fixing
rate. The original research showed that the fixing rate
reached a peak at some concentration and became longer for
greater concentration. The film used for these tests was dry
when it entered the fixing bath. Later research showed that
when the film was wet no peak was found and that fixing rate
continued to increase with Thiosulfate concentration. Since
the film or paper is wet in normal processing it makes sense
(at least to me) to have it in wet condition when testing.
Toning: It was found in research at the Image Permanence
Institute nearly twenty years ago that Kodak Rapid Selenium
Toner was no longer providing adequate protection to
microfilm when used in the then recommended dilution of
1:19. The effect may not carry over to other types of
emulsion but paper emulsion is similar to Microfilm in being
relatively slow, very fine grain, and quite thin. The reason
was that the toner was not toning all densities equally and
left low density areas vulnerable to oxidation and
sulfiding.
It was determined that a better toner for protecting
microfilm was a sulfiding toner using Liver of Sulfur such
as Kodak Brown Toner. IPI came up with a modified form of
toner for microfilm use which was relatively odorless but
KBT and Kodak formula T-9 are perfectly effective. These
toner have the advantage of toning all densities at the same
rate so will provide protection even when only partial
toning is done.
In a personal communication from Dr. Nishimura, of IPI,
he states that KRST will also provide adequate protection
for prints if used in a dilution of no greater than 1:9 and
for a toning time of not less than three minutes. The
original recommendation for the highly diluted toner was
made because it has little effect on image color or density,
and, important for microfilm, has little or no effect on the
image structure. IPI speculates that the original toner
results were due to incidental sulfiding by some impurity in
the toner. Kodak claims the formula and method of making
KRST was not changed.
Either a stong solution of KRST or a normal dilution of
KBT will cause stains if fixing is not adequate so, when
toning is routine, both form a sort of automatic test for
residual silver as a result of incomplete fixing.
The use of either strong KRST or KTB will pretty much
eliminate problems from airborne polutants on displayed
prints.
Beside testing for silver complex residues the prints
should also be tested for remaining thiosulfate. This is
done using a solution of Silver Nitrate preserved with
Acetic acid. This is a test for adequate washing and will
show up problems with washing devices. While this test can
be made on spots in the same way as the residual silver test
it is probably a good idea to test at least once on a
complete sheet of paper to see if the washing is uniform in
all areas. The test produces a stain similar to that left by
the residual silver test and the same comparison chart can
be used for both.
A final note: The retarding effect on washing of acid
fixing baths and hardening fixing baths is eliminated by the
use of a buffered Sulfite wash aid such as Kodak Hypo
Clearing Agent. When this treatment is used the wash rates
following any type of fixing bath will be very nearly the
same.
---
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:
