[pure-silver] Re: fixer question
- From: Richard Knoppow <dickburk@xxxxxxxxxxxxx>
- To: pure-silver@xxxxxxxxxxxxx
- Date: Tue, 3 Jun 2008 06:24:28 -0700 (GMT-07:00)
-----Original Message-----
>From: Charlie Thorsten <charlie_thorsten@xxxxxxxxx>
>Sent: Jun 3, 2008 1:40 AM
>To: pure-silver@xxxxxxxxxxxxx
>Subject: [pure-silver] Re: fixer question
>
>--- On Mon, 6/2/08, Sissy Albertine <salbert@xxxxxxx> wrote:
>
>>Hi all,
>>I am printing on Ilford Multigrade FB paper and noticed the directions >state
>>that it should be fixed in Ilford Paper Fixer (1 + 3) for 1 minute >with
>>intermittent agitation. Being old school, I find it hard to believe >fiber
>>base can be archivally fixed in 1 minute. Am I off here?
>>Thanks,
>>Sissy Albertine
>
>Ilford did a lot of research into how to achieve shorter
>washing times, mainly because much of England tries to
>conserve water and a 1-2 hour wash was prohibitive. They
>found that a 1 minute fix in FRESH rapid fixer (ammonium
>thiosulfate), mixed 1:4, with CONSTANT agitation allows
>complete fixing of the emulsion without too much fixer
>penetrating the paper base. This allows a washing time
>of 30 minutes, or a 5min wash/10min HypoClear/5min wash
>cycle (See Ilford fact sheet "Processing B&W FB Paper":
>http://www.ilfordphoto.com/Webfiles/200621111117720.pdf)
>
>This works only if you follow the rules exactly. The print
>must be fixed vigorously for precisely one minute. Any
>longer and fixer will saturate the paper base, negating
>any short wash advantage. Second, the rapid fixer bath
>(ammonium thiosulfate) must be FRESH. Ilford specifies a
>capacity of only 10 8x10's per liter of working solution.
>Remember this includes all test strips, work prints, etc.
>
>It definitely works if this is followed precisely, but it's
>easy to mess up. Two bath fixing followed by a longer wash
>(one hour) is far more reliable and more forgiving. It
>mainly depends if you're trying to save water or not. The
>"old school" way is not wrong by any means.
>
>-Charlie
>
>
This works for some Ilford papers that will fix out in one minute or less.
The original process specified 30 seconds fixing time. Many papers especially
some now discontinued Kodak papers will not fix quickly enough.
The idea is that the sort fixing time prevents the fixer from being taken
up by the fiberous structure of the paper as you state. While the emulsion can
be washed out very quickly, especially if a sulfite wash aid is used, the paper
tends to bind the thiosulfate by mechanical means requiring frictional forces
to remove it. Sulfite wash aid, which has an ion exchange property for
thiosulfate, can help but is much less effective for removing it from the
support than from the emulsion and substrate. As a result even with an extended
treatement with wash aid (Ilford recommends ten minutes) the wash time is still
longer than for film or RC paper.
The ability of a single fixing bath to completely fix out (make soluble)
the silver halide remaining after development is _very_ limited. Actually the
capacity stated by Ilford is not 10 8x10 sheets per liter but per _gallon_.
This astonished me when I first read it but was confirmed by someone at Ilford.
Ilford recommends using rapid fixer without hardener at the dilution
recommeneded for film.
Ilford's motive for devising this fixing and washing method was not so
much to save water as to insure long image life by insuring washing conditions.
However, it does save water as does the successive bath method of washing
rather than running water.
Its probable that the normal processing using what I will call the Kodak
method results in equally permanent images. This requires fixing in two
successive fixing baths, a treatment with a buffered sulfite wash aid, and
running water or successive bath with constant agitation washing.
The use of two successive fixing baths is very important because it very
much extends the capacity of the bath. Kodak estimates the capacity is extended
from four to ten times. Some have stated here that two bath fixing is not
necessary when using ammonium thiosulfate fixer but I suspect is safer to do
so.
Note that it is NOT necessary to remove all thiosulfate from the emulsion.
A very small residue of thiosulfate has been found to act as a stabilizer
preventing oxidation of the image. It is not as effective as toning but
research done at Kodak Research Labs and at Fuji found that film or prints
which had been completely freed of residual hypo were much more vulnerable to
oxidation than those with some remaining hypo.
However, the presence of residual halide and fixer reaction products is
always harmful. While the use of a buffered sulfite wash aid will help remove
some incompletely converted reaction products it will not take the place of
reasonably fresh fixer.
The best test as mentioned in my original post is to check for the
residual silver by using a stain test. There is a test for silver concentration
in the fixing bath but it is indirect and does not indicate when the fixer has
stopped fixing. The sulfide or selenium test does.
If one expects longevity for prints or film, but especially for prints,
they should be toned. This is very especially true of prints to be displayed
since they are exposed to the air for long periods. Most of the damage will
come from polutants in the air. Suitable toners are:
Any sulfiding toner but especially polysulfide toners like Kodak Brown Toner,
unless the prints are to be toned to completion. KBT and similar toners do not
split tone so that incomplete toning will still protect all densities.
Gold toners are very effective and are the standard for microfilm. Again,
the image must be sufficiently toned if it is to be protected. The current
recommendation for microfilm is a polysulfide toner partly because gold toners
are expensive.
Kodak Rapid Selenium Toner is suitable provided toning is carried out far
enough. For many years KRST was the recommended treatment for microfilm,
especially at high dilution (1:19) because it was thought to provide a very
high degree of protection without altering the color or structure of the image.
However, about twenty years ago it was found that KRST was no longer effective.
The exact reason for this has never been definitely discovered. Kodak claimed
the formula and method of manufacture had not changed but its possible that
some of the protective action may have been due to impurities which disappeared
when the source of supply for some component was changed. That is speculative
and, according to Dr. Nishimura of IPI, one of the investigators, the true
cause has never been determined.
KRST at high dilutions does not completely protect images because it tones
high densities before low densities. So, when used according to the old
recommendations the lighter parts of the image remain suseptible to oxidation.
According to Dr. Nishimura complete protection is possible provided film or
prints are toned in a solution of no weaker than 1:9 dilution and for not less
than 3 minutes at room temperature. This, however, does cause some change in
color for some materials.
If any of these toners are used its important that the film or prints be
well fixed and washed otherwise the toners will affect the residual silver
compounds as well as the image and cause staining.
The procedure of diluting KRST with wash aid should be abandoned. It works
only at high dilutions and, as pointed out, these do not work. Well washed
prints will be at the pH of the wash water regardless of whether an acid or
neutral fixer has been used. However, the use of a buffered wash aid will
deliver them to the wash water at neutral pH. Selenium toner is capable of
leaving a n overall stain from precipitated elemental selenium toner if the
print or film is strongly acid when introduced into the toning bath. This is
probably never a problem when the material has been well washed before toning.
When KHCA is used according to Kodak instructions the wash time for film
is no more than 5 minutes, no more than 10 minutes for single-weight paper, and
no more than 20 minutes for double-weight paper. The time is not too critical
as long as it meets these minimums but should not be long extended due to the
protective effects of residual hypo as noted above. This is probably of no
significance when the material is properly toned for permanence.
Note that both Agfa and Fuji sold "stabilizers" for use in protecting
images when toning was not desirable because of changes in the image. Fuji
published a limited amount of research data on their stabilizer showing to be
effective but less so than toning. AFAIK, there has never been any formalized
investigation of its performance published on the Agfa product (Sistan)
although there may very well be something I am not aware of. The Fuji product
(Ag-Guard) is sold only in Japan. Agfa changed the recommended method of using
their product a couple of times because excessive take up can cause eventual
staining.
Toning can be applied to film and prints both on fiber and RC base. While
modern RC paper does not seem to have the problems with short image life that
were reported some years ago toning will still provide considerable protection
to them.
--
Richard Knoppow
dickburk@xxxxxxxxxxxxx
Los Angeles, CA, USA
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