[pure-silver] Re: Formula #87 in Anchell
- From: "Richard Knoppow" <dickburk@xxxxxxxxxxxxx>
- To: <pure-silver@xxxxxxxxxxxxx>
- Date: Mon, 16 Jan 2012 20:29:58 -0800
----- Original Message -----
From: "Bogdan Karasek" <BKarasek@xxxxxxxxxxxx>
To: <pure-silver@xxxxxxxxxxxxx>
Sent: Monday, January 16, 2012 5:34 PM
Subject: [pure-silver] Formula #87 in Anchell
Hello all,
Just needed some advice from those who know about such
things....
More and more, I find myself mixing my own chemicals. For
paper, I can now get Hypo (Sodium Thiosulfate) in 25kg
bags from a chemical firm. I use the 2 tray method of
fixing. But what about film? I checked Anchell and found
this interesting formula (#87 Odourless Acid Hardening
Finishing Bath for film or paper)
I have all the ingredients:
Sodium Thiosulfate, 240gr
Sodium sulfite (anhydrous), 15.0gr
Acetic Acid 28%, 48.0ml
Balanced Alkali, 15gr
Potassium Alum, 15gr
Water to make make one Litre.
I don`t have any Potassium Alum , but Anchell tells me
that the Potassium Alum is the hardening agent in the
solution, so if I leave it out, do I have a fixer that
is non-hardening?
Am I correct in this assumption and can I proceed without
the Potassium Alum. I will be mixing 17 Litres in tanks
for 8x10 Tri-X.
Later, I want to develop some 4x5 Efke PL 25 Otho. The
Efke emulsions tend to be soft and a hardening fixer is
recommended.
Is there a commercial name for Potassium Alum, something I
could get at the pharmacy or supermarket, so I could use
it with the Efke fixer, or am I still good without the
Alum?
Can I substitute Baking Soda for the Balanced Alkali, and
if so, in what proportion, or are they interchangeable in
terms of quantity?
Cheers,
Bogdan
Jean David has already pointed out that this is Kodak
F-6. The main difference between this and Kodak F-5, which
is the standard formula is the use of Kodalk Balanced Alkali
AKA sodium metaborate in place of borax.
A couple of notes: Sodium thiosulfate will fix all by
itself but will oxidize rapidly without the addition of some
sodium sulfite to protect it. The sulfite has the further
effect of preventing staining from developer reaction
products since the developer will continue to be active
until the hypo dissolves enough halide. If a plain, non-acid
bath is desired about 5 grams per liter of sulfite is
sufficient. In hardening baths enough additional sulfite is
added to prevent the thiosulfate from being decomposed by
the necessary acid typically about 15 grams per liter.
Thiosulfate will fix regardless of the pH of the bath
its in but the inorganic hardeners often used require the
bath to be acid to work. The most common hardener is
potassium aluminum sulfate more commonly known as alum or
white alum. A few fixing bath formulas call for chrome-alum
which is potassium chromium sulfate. Chrome alum results in
more complete hardening of the emulsion but can produce
staining so it was never used for printing paper. It was
most often used for high-temperature processing.
The use of acid in a fixing bath even without the
hardener has some advantage, mostly that is stops the
developer immediately, allowing more controllable
development, and also prevents the generation of reaction
products by the residual developer. The disadvantage of acid
is that it tends to prolong washing. The rate at which
thiosulfate diffuses out of the emulsion depends partly on
the relative electrical charge of the molecules of the
emulsion, when acid the charge tends to attract, thus bind,
the thiosulfate ions; when neutral or alkaline, the charge
tends to repel the thiosulfate ions. In addition white alum
hardener has a specific mordanting property for both
thiosulfate and its reaction products. The effect takes
place only when the emulsion is acid. However, the hardening
also is effective only as long as the emulsion is acid.
While both the mordanting and electrical binding can be
eliminated by treating the emulsion in an alkaline bath such
a bath will also destroy the hardening. However, both
mordanting and charge binding are eliminated at neutral pH
(for typical photographic gelatin) while the hardening is
preserved. So, treating in a wash aid which produces a
neutral condition will accelerate washing without destroying
the hardening. The use of sulfite as a wash aid has the
advantage over other alkalis that it has an ion exchange
effect on the thiosulfate so accelerates washing even when
the emulsion has been fixed in a neutral or alkaline fixing
bath.
Almost all standard fixing baths have about 240 grams
per liter of crystalline sodium thiosulfate in them.
Anhydrous thiosulfate works as well and less is necessary.
However, most fixer formulas were written at a time when the
crystalline form was the most available. The reason for this
quantity traces to research done at Kodak a very long time
ago. The first research into the optimum amount of
thiosulfate was done with dry film. It turned out that the
condition of the emulsion is important: when the experiments
were repeated some years later with wetted film it was found
that the rate of fixing Vs: hypo concentration did not reach
a peak at 240 grams, as shown in the first experiments, but
continued to become shorter as the concentration was
increased. Nonetheless, the amount became a standard and
continues to the present.
The use of ammonium thiosulfate in place of sodium
thiosulfate results in a fixing bath that is faster and less
sensitive to the accumulation of reaction products. This was
known for decades but "rapid" fixer was not popular because
ammonium thiosulfate in dry form is not stable and liquid
concentrate is expensive. Also, when made acid, as in a
standard fixer formula, ammonium thiosulfate tends to
dissolve fine metallic silver particles resulting in
bleaching unless fixing time is carefully regulated. This
also made it difficult to use in a hardening bath since the
hardener might take considerably longer to work than the
fixer. BTW, the slowness of the hardener is one reason that
older instructions often specify extremely long fixing
times. Fresh sodium thiosulfate fixer will fix out most
emulsions in a couple of minutes but the hardener may need
ten or more minutes to work. Even tabular grain film
emulsions may fix out faster than is necessary for hardening
and certainly film-strength rapid fixer will.
Note also that all acid fixing baths contain an acid
buffer combination. This is to maintain the pH in a range
where the hardener will work. It is to compensate for
carried over developer and also carried over stop bath. If
its desired to keep the development stopping property even
in a non-hardening bath a buffer is still necessary to
prevent the fixer from becoming alkaline from carried over
developer or too acid from carried over stop bath, which
could cause decomposition. Where an ammonium
thiosulfate bath is used without acid, or with reduced acid
in a non-hardening bath the bleaching effect does not take
place so it can be used full strength for even warm tone
papers without affecting either density or image color.
A rapid fixer can be made by the addition of ammonium
chloride to a conventional fixing bath, as in Kodak F-7, but
is not as satisfactory as a bath made with ammonium
thiosulfate.
A good non-hardening fixing bath with reduced acidity
is Kodak F-24 given below. Because of the fairly high pH
there is less tendency for this bath to produce sulfur
dioxide gas, the familiar hypo odor, which many find
particularly irritating.
Kodak F-24
Water (at about 125F).............500.0 ml
Sodium thiosulfate, crystalline...240.0 grams
Sodium sulfite, desiccated.........10.0 grams
Sodium bisulfite...................25.0 grams
Water to make.......................1.0 liter
Note: if anhydrous thiosulfate is used the water temperature
should not be over about 90F to prevent decomposition.
Crystalline hypo is extremely endothermic and will rapidly
cool the water its mixed in.
Sodium thiosulfate, crystalline had an approximate
formula weight of 248 and anhydrous of 158 so that if you
want to use anhydrous in place of crystalline the ratio is:
64%
I don't have formula for rapid fixers at hand but
ammonium thiosufate can be substituted for sodium
thiosulfate in standard formulas by conversion of amounts
using the formula weights. Formula weight for ammonium
thiosulfate anhydrous is 148.2. Typical liquid concentrates
are about 58%. My memory is that rapid fixers have rather
more thiosulfate in them than standard fixers.
Another note: sodium metaborate can be made by
combining borax and sodium hydroxide in solution. The
amounts are: Sodium hydroxide....14.5 grams, borax, 69
grams, equals 100 grams of sodium metaborate. Adjust these
amounts according to the amount of metaborate you need in
the formula.
I didn't really mean to write a treatise when I started
out but the fit was upon me.
--
Richard Knoppow
Los Angeles, CA, USA
dickburk@xxxxxxxxxxxxx
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