[pure-silver] Re: Non-acid rapid fixer - continued
- From: "Richard Knoppow" <dickburk@xxxxxxxxxxxxx>
- To: <pure-silver@xxxxxxxxxxxxx>
- Date: Thu, 18 Feb 2010 09:13:05 -0800
----- Original Message -----
From: "Claudio Bonavolta" <claudio@xxxxxxxxxxxx>
To: "Pure-Silver" <pure-silver@xxxxxxxxxxxxx>
Sent: Thursday, February 18, 2010 4:15 AM
Subject: [pure-silver] Non-acid rapid fixer - continued
Following my quest for a non-acid rapid fixer due to my
sensitivity to sulphur dioxyde, I would like to thank all
of you who replied either through the list or directly.
I finally got the raw chemicals and modified my process
to:
- developer
- citric (15gr/l) acid stop bath
- rinse
- Kodak F-9 modified (see below) fixer in 2 baths
- rest of the process
The original F-9 formula is the following:
Water 600ml Hot water
Sodium Thiosulfate 360gr crystalline or 230gr
anhydrous
Ammonium sulfate 60gr
Sodium Sulfite (anhydrous) 15gr
Acetic Acid glacial 13.5ml
Boric Acid 7.5gr
Potassium Alum (fine dodecahydrated) 15gr Do not use
anhydrous
Cold water to make 1000ml
As you can see, it's a hardening formula which I don't
need.
The simplified formula I use is the following:
Water 600ml Hot water
Sodium Thiosulfate 360gr crystalline or 230gr
anhydrous
Ammonium sulfate 60gr
Sodium Sulfite (anhydrous) 15gr
Cold water to make 1000ml
Bob Kiss suggested to add 5gr/l of sodium metaborate as to
keep the solution on the alkaline side. As I wasn't able
to find the metaborate (tried two chemical distributors,
both were out of stock ...), I started without it, will
add it later.
The good thing is that, as the dilution of the sodium
thiosulfate looks endothermic (absorbs heat), the
temperature cools down and you can use it quickly after.
So, no need to prepare it long in advance.
I was also looking for a fast fixer. Fast fixers are
normally based on ammonium thiosulfate but F-9 is
described as being fast *and* based on the more readily
available sodium thiosulfate.
So I compared the F-9 modified formula to Ilford Rapid
Fixer at 1+4 (typical film strength) by putting a film
leader in each and measuring the time it took to clear.
I used of course the same film type from the same lot
(from a bulk roll) and the temperature of both fixers was
identical.
The clearing was just slightly slower, a few seconds, in
the F-9, so, from a practical point of view, I just keep
the same fixing times.
Looks like the ammonium ions coming from the sulfate are
making the difference but my limited chemical skills do
not allow me to be affirmative on this.
For those who tone the prints in selenium, because the
fixer is no more acid, the risk of stains has gone and
there is no need to wash the prints between the fixer and
toner, I just put a rinse between them.
I continue to use a washaid (sodium sulfite @ 20gr/l
discarded at the end of the session) before the final wash
as to keep the wash times and water consumption at the
minimum.
On the smell and sulphur dioxyde side, I'm really happy,
my lungs confirmed this is the way to go ...
Note that before the non-acid fixer, I tried also to put a
rinse between the stop bath and an acid fixer and it
already diminished the quantity of sulphur dioxyde that
was released but there was still some coming from the
fixer alone.
The next steps on the fixer side are to put in place an
efficient and practical way of measuring the exhaustion of
the fixer and quality of the fixing. I was used to use the
potassium iodide test (very easy to do) but seen the
recent "Fixer test vs fixer test" discussion, I'll have to
re-think it and try to see if I can relate in some ways a
more accurate test but more cumbersome (selenium test) and
the easy potassium iodide test.
Claudio Bonavolta
http://www.bonavolta.ch
A simple formula for a sodium thiosulfate fixer is as
follows. For rapid fixer ammonium thiosulfate is substituted
for the sodium thiosulfate in appropriate amount. Ammonium
thiosulfate is usually sold as a liquid concentrate because
the powdered version has a short shelf life.
Simple non-acid, non-hardening fixing bath.
Water 500.0 ml
Sodium thiosulfate, crystalline 240.0 grams
Sodium sulfite, desiccated 5.0 grams
Water to make 1.0 liter
The sulfite can be increased up to about 15 grams/liter to
permit the use of an acid stop bath. The additional sulfite
will prevent decomposition of the thiosulfate by the acid. A
citric acid stop bath can be used with this fixer.
However, any acid carried over into the fixer may
result in some sulfur dioxide being emitted.
--
Richard Knoppow
Los Angeles, CA, USA
dickburk@xxxxxxxxxxxxx
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