[pure-silver] Re: fixer question
- From: "Richard Knoppow" <dickburk@xxxxxxxxxxxxx>
- To: <pure-silver@xxxxxxxxxxxxx>
- Date: Mon, 2 Jun 2008 16:27:58 -0700
----- Original Message -----
From: "Sissy Albertine" <salbert@xxxxxxx>
To: <pure-silver@xxxxxxxxxxxxx>
Sent: Monday, June 02, 2008 8:51 AM
Subject: [pure-silver] fixer question
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
It can be with a couple of caviats. The emulsion of RC
paper is very thin and there is nothing under it to absorb
any of the emulsion when its coated. The paper fixer is a
"rapid" or ammonium thiosulfate fixer, I am not sure of the
concentration of the Ilford product but, in general,
ammonium thiosulfate fixers are faster than sodium
thiosulfate fixer, but it depends on the concentration.
When using sodium thiosulfate fixer the fixing time for
most RC papers is 2 minutes. I use two baths and fix in each
for one minute. Ammonium thiosulfate fixer has a somewhat
higher capacity for complete fixing than the sodium form so
one can use a single bath but I would check with Ilford as
to what the capacity of this particular fixer is.
The silver halide in paper or film emulsion is not
soluble in water so the undeveloped halide which remains
after development must be converted into a soluble substance
in order that it can be removed. This is the job of the
fixer. The process is stepwise with each step being
increasingly more soluble. However, there must be enough
thiosulfate ions available in the fixing bath to complete
the process. It takes three thiosulfate ions to combine with
one silver halide ion to convert it. Since a lot of the
silver halide comes out in the fixer after a certain amount
of emulsion is fixed there are no longer enough ions left to
complete the fixing process. The film or paper my be
"cleared" (film looks cloudy when there is halide left) but
there may still be enough halide or insoluble fixer reaction
products left to react with the image in the future causing
staining.
The safest way around this is to use two successive
baths, each for half the recommended fixing time, and to
check the prints or film with a residual silver test
occasionally. A two bath system has anywhere from four to
ten times the capacity for complete fixing as a single bath
so its an ecomomy as well as good insurance.
The residual silver test is simply a solution of dilute
sodium sulfide (not sulfite) or, alternatively a 1:9
dilution of Kodak Rapid Selenium Toner can be used. A drop
or two is placed on a clear area of the film or paper while
it is still wet and allowed to stand for about two minutes
and blot off. This will tone any remaining halide was well
as it tones silver so it will leave a yellow or brown stain
if there is incomplete fixing. For paper its a good idea to
fix out a scrap of paper along with your prints and test on
that because the test will produce a stain with time even if
the emulsion has been completely fixed. Since negatives
usually have a clear border around the image you can test
there, where a stain won't show, and not have to fix a film
scrap. If the test is positive the prints or film should be
re-fixed in fresh fixer. This must be done quite soon after
the original processing since the nature of the fixer
reaction products changes with time. After about two weeks
it is no longer removable by re-fixing.
For film or fiber base paper the use of a sulfite wash
aid, like Kodak Hypo Clearing Agent, will extend fixer
capacity even more since it is capable of debonding some
otherwise insoluble reaction products. However, RC paper,
with its thin emulsion and non-absorptive substrate and
support, will wash out so fast that the use of wash aid is
not necessary unless you find you have toning problems.
---
Richard Knoppow
Los Angeles, CA, USA
dickburk@xxxxxxxxxxxxx
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