Fixer Question

[taco*boy]

Is fixer OK to use over and over and over? I've heard that fixer will turn
purple when depleted. I have never seen this. Am I wasting fixer I throw it
away and it's still clear?

Thanks,

Scott

[Michael Gudzinowicz]

The best option is to use two bath fixation. The rationale is outlined
below, taken from one of my old posts.


Post Development Processing

Copyright 1998 by Dr. Michael J. Gudzinowicz

The basis of fixation and accompanying problems aren't treated in depth in
most texts. This oversight often leads to postponed "accidents" whenever
people are tempted by a sense of false economy to save time or materials. An
introduction to the underlying chemistry should help to define a more
critical approach to film and paper preservation, which doesn't rely on
rumor and the advertising literature. The following notes were taken from
Grant Haist's "Modern Photographic Processing, Vol.1" (Wiley, 1979), "The
Theory of the Photographic Process" edited by T. H. James (3rd & 4th ed.,
1st & 2nd edited by C. E. K. Mees; Macmillan, 1966 (3rd)), "Ilford
Monochrome Darkroom Practice" by Jack Coote, and the research and technical
literature.

Fixation:

The common notion is that the fixer removes undeveloped silver halide by a
simple reaction involving the replacement of the halide by thiosulfate to
form a soluble silver complex, and then if the film or paper looks or tests
"clear", the only problem is fixer removal. Unfortunately, this is not the
case. When a film is "fixed", a number of complexes are formed between
silver and thiosulfate, and all are in dynamic equilibrium. In addition, the
accumulation of halide during fixation reduces fixer capacity with use when
free silver and halide levels approach their limits of free, non-complexed
solubility.

A simple table outlining the dissolution of silver in fixer, and equilibria
with fixer is outlined below.

The silver halide may dissociate to a very small degree in aqueous
solutions, and the thiosulfate anion will form a 1:1 complex with the silver
cation (Rxn 1) or the thiosulfate may react directly with the solid silver
halide crystal (Rxn 1). In either case, the first complex (I) is >very
insoluble< and remains tightly adsorbed to the surface of the solid silver
halide.

A second thiosulfate anion may react with the first complex (I), to form
a soluble product (II) with a silver to thiosulfate ratio of 1:2 (Rxn
2); and then if "free" thiosulfate concentrations are high, a third
thiosulfate anion may react with the soluble second complex (II),
creating a third complex (III) with one atom of silver and three
molecules of thiosulfate which is quite soluble (Rxn 3).


Sequence of Complex Formation:

Note: Charge of ions is in () brackets; the # of kinds molecules [kind of
molecule]# in the complex follows brackets; TS is thiosulfate (hypo) anion;
Ag is silver; Br is bromide. <-> shows equilibrium reactions.

Rxn 1) Ag (+) + TS (-2) <-> AgTS (-)

AgTS (-) is the first complex (I) called monoargentomonothiosulate since it
contains one silver cation and one hypo anion; it is insoluble and remains
adsorbed to the crystal as it forms.

Rxn 2) AgTS (-) + TS (-2) <-> Ag[TS]2 (-3) (aq)

Ag[TS]2 (-3) (aq) is the second complex (II) complex formed by the addition
of another thiosulfate anion to monoargentomonothiosulate to form
monoargentodithiosulfate. The second complex is soluble in aqueous solutions
and is removed from the emulsion by diffusion.

Rxn 3) Ag[TS]2 (-3) (aq) + TS (-2) <-> Ag[TS]3 (-5) (aq)

Ag[TS]3 (-5) (aq) is the third complex (III) called
monoargentotrithiosulfate since it has three thiosulfate anions complexed
with one silver cation. It very soluble in aqueous solutions.

In solution, these reactions are reversible, so all complexes are
present, and a small amount of Ag+ cation is not complexed in solution.

The following equilibria also occur:

Rxn 4) Ag (+) (aq) + TS (-2) <-> AgTS(-) (aq)

where all components are in solution (aq) and adsorption doesn't occur.

Rxn 5) AgTS (-) (aq) + TS (-2) <-> Ag[TS]2 (-3) (aq)

where the monoargentomonothiosulfate is in solution and not adsorbed.
However, in solution the concentration of monoargentomonothiosulfate in this
and the preceeding aqueous reactions are very low since it's nearly insoluble.

Rxn 6) Ag[TS]2 (-3) (aq) + TS (-2) <-> Ag[TS]3 (-5) (aq)

where both the monoargentodithiosulfate and monoargentotrithiosulfate
complexes are in solution.

As more silver is put into solution with fixer use, more complexes II & III
are formed, and the level of the less soluble 1:1 complex (I) and free
silver ion are also increased. After a few uses of fresh fixer, the less
soluble complex (I) and silver halide are left in the paper or film at low,
but destructive levels, although the film appears to clear.

Also, thiosulfate is adsorbed to developed silver grains in papers (iodide
tends to displace it from films). Residual complex I and residual
thiosulfate adsorbed to developed silver grains are converted to trithionite
and higher thionites in a few days, and then degrade and react with silver
giving stains (sulfiding) and fog. (Brown silver sulfide is seen after
bleaching the silver grains, and is proportional to the developed silver.)

With progressive use of the fixer, levels of bromide rise, as well as
chloride from papers and iodide from films. Silver halides have very low
solubility, and as the level of bromide or iodide rises, it forms silver
halide crystals in solution and the fixer will no longer dissolve silver
halide. A number of complexes and equilibria occur with each halide and
mixtures. On a relative basis, silver chloride is more soluble than bromide
and has little effect on fixer capacity; silver bromide is less soluble and
determines fixer activity to a significant degree, unless films containing
low levels of iodide are fixed, in which case fixer capacity is reduced
significantly due to silver iodide insolubility (a problem with T-Max films,
treated later). In instances where silver is removed to "regenerate" fixers,
iodide accumulation may interfere. Also, in two-bath fixation which follows,
carry-over occurs, which requires periodic replacement of both baths.

The only way to ensure that little silver bromide (AgBr) or the insoluble
first complex is left in the paper, is to use fresh fixer with little
accumulated silver and halide, and an excess of non-complexed free
thiosulfate to remove it. This approach to archival fixing when used with
one bath is fairly wasteful, though effective.

Rather than using one bath, the same results can be obtained with two baths,
and the capacity of the fixer is far greater. Essentially, the first bath
removes the bulk of the silver and halide, and leaves traces of silver
halides and the first insoluble complex in the emulsion and paper. The
amount when carried over to a second bath is insignificant in comparison to
the amount of free thiosulfate, so the second bath always acts as "fresh"
fixer with high non-complexed thiosulfate levels to react with the small
amounts of silver halide and less soluble complexes to speed their complete
removal from the emulsion.


More on Fixing - One and Two Bath Fixation:

Grant Haist, the former director of research at Kodak, cites the following
maximal permissible values for one-bath film and paper fixers for commercial
and archival processing:

One-bath fixation: Commercial Archival

Film:

Max. Ag conc.: 1.5 g/l 0.2 g/l
Max rolls/gal: 25 rolls/gal 2 rolls/gal
Non-image Ag in film: 0.01 mg/in^2 0

Paper:

Max. Ag conc.: 0.3 g/l 0.05 g/l
Max. sheets/gal: 30 8x10 5 8x10
Non-image Ag in paper: 0.005 mg/in^2 0

Essentially, as fixer total silver (free and complexed) and halide
concentrations rise, the fixer's ability to remove all of the silver from
the paper diminishes markedly, as indicated by the very limited capacity of
one-bath to remove silver to archival levels.

The solution to the limited capacity is to use a fresh second fixer bath to
maintain a very low total silver level, with a water rinse between the first
and second baths to minimize fixer/silver carry-over. Some older texts even
suggest a fresh third bath.


Two bath fixation: Commercial Archival

Film:

Bath 1:
Max. Ag conc.: 6 g/l 3.5 g/l
Max. rolls/gal: 60-70 40

Bath 2:
Max. Ag conc.: 0 .5-1.5 g/l 0.02 g/l
after 60-70 after 40

Non-image Ag in film: 0.01 mg/in^2 0


Paper:

Bath 1:Max. Ag conc.: 2 g/l 0.8 g/l
Max. sheets/gal: 200 8x10 70 8x10

Bath 2:
Max. Ag conc.: 0.3 g/l 0.05 g/l
after 200 after 70

Non-image Ag in paper: 0.005 mg/in^2 0

The first fixer gets rid of most of the silver, and the second maintains a
very low silver concentration and relatively high free thiosulfate
concentration to remove the remainder of the insoluble complexes and
non-image silver present in the emulsion after the first fixation.

The first bath is used for the maximum number of sheets or rolls indicated,
and then discarded after silver recovery.

The second bath is substituted for the first, and a fresh second bath is
prepared.

After 5 cycles (substitutions), or one week if continuously exposed to air
in tanks, both baths are replaced. Compare the capacity for commercial or
archival standards using two baths to that for one. Two bath fixation is far
more economical than using one bath, and avoids the temptation to over-use
fixer which results in under-fixation and difficult removal of insoluble
complexes which destroy prints and film.


Films:

With films, the fixation time in the first fixer should be at least
twice the clearing time... likewise for the second bath.

The clearing time should be checked often if that approach is used, however,
Kodak recommends 5-10 minute fixation with non-rapid fixers and most films.

Since there is _no_ danger in longer fixing times, incorporating a five minute
minimum fix in each bath into a "normal" development procedure may avoid problems
and provide some security.

Agitation should be constant to remove fixer from the surface of the film to
facilitate diffusion, however, increased agitation never can replace
adequate fixing time or counteract the cumulative effects of re-using fixer.

With rapid fixers, there is little "danger" of bleaching film with 5-10
minute fixation. Also, if standard procedures are used, any minimal
bleaching would never be noticed, since it would be incorporated into tests
for contrast and development time.

With T-Max films, Kodak recommends longer times. For instance, they suggest
that it is "safe" to check clearing at five minutes with standard fixers or
three minutes with rapid fixers, and that total fixing time should be twice the
clearing time. (Kodak's "advice" on T-Max varies from simplistic on 35 mm
film boxes, to warnings in detailed technical literature, not only on times,
but also on fixer replenishment rates for processors.)


T-Max Films:

With some films, such as Kodak's T-Max series, fixer capacity is reduced to
one-half of what one normally expect, and fixing times are extended to twice
the usual time, since silver iodide present in the "high tech" emulsions is
resistant to fixation, and exceedingly insoluble.

In Kodak publication F-32 on T-Max films, Kodak indicates that a magenta
stain may be left in the emulsion with inadequate fixing, and recommends
further fixing with fresh fixer to remedy the problem. The magenta
sensitizing dye is adsorbed to the silver halide (EKC statement - not
speculation) and when the halide is fully dissolved, the dye is removed.

In some instances, the dye can be removed by treatment with hypo-clear,
which usually contains sulfite or high salt concentrations which can act as
weak fixers in addition to displacing hypo, or with prolonged water washes.

The "stain" problem isn't whether it will interfere with variable contrast
paper filtration or not, but its indication that the film isn't fixed
properly.


Papers:

For paper fixation, do not use fixer which has been used for film. It is
difficult to track capacity accurately (see table above... silver capacity
differs for film and paper), fixer dilutions vary between paper and film
fixers, and the "sudden" accumulation of iodide after developing films may
greatly prolong paper fixation or leave insoluble silver iodide behind.

The clearing time for papers may be determined experimentally or by
manufacturer recommendation (for Ilford, see below). Fixing times for
most fiber papers is on the order of five minutes for each bath, with an
intervening water rinse and storage in water. To save time, prints can
be fixed in the first bath, rinsed and held in water, then fixed in the
second bath at the end of a session. Long contact with fixer can cause
problems if fixer enters the paper fibers (not between them). Papers and
fixers vary, and it is best to use at least the minimum time recommended by
the paper manufacturer.

Kodak recommends 10 min for fiber base and 2 min for RC in one bath, or half
that time for each of two baths. The RC time is optimistic, though five
minutes per bath is reasonable for fiber papers. Prolonged contact with
rapid fixers will slowly bleach an image or cause uneven bleaching if prints
remain in rapid fix without agitation for prolonged times (hours).

In any case, paper and film should be promptly removed from the second
fixer, rinsed, and placed in a water bath until treated with a hypo clearing
solution to displace free thiosulfate.


Rapid Fixer:

Rapid fix has the advantage of a shorter contact time, and that may
minimize the penetration or degradation of fixer in the paper's fibers.

Also, the useful capacity of rapid fixers is fairly high... 10-15 g/l
silver vs. 6g/l for films or 2 g/l for papers using regular fixers
(James; Haist table above for bath 1 of a two bath sequence).

However, there is little data to extrapolate those numbers into increased
capacity _without risk_ of problems. In that regard, Kodak's recommendation
for capacity of rapid fix and other fixers is nearly the same (100-120
sheets or rolls), which is optimistic for one bath commercial processing.
The only advantage of rapid fix with film is decreased processing time and
perhaps, decreased rinse time.


Hardeners:

For film, a hardening fixer is often preferred to minimize any emulsion
damage in handling and to avoid reticulation. Very alkaline developers can
remove the manufacturer's hardeners. If the emulsion is loaded with salts
such as fixer, and placed in plain water, the emulsion can swell markedly
due to water uptake in the emulsion due to osmotic pressure. If the water is
warm, the emulsion may ripple on the surface, giving the alligator pattern
associated with reticulation.

Non-hardening fixers are often preferred for development of the stain with
pyro developers.

For paper, rapid fix without hardener is often preferred, and gives
better results with toning. Paper curl seems to be minimized and there
is less danger of "breaking" the emulsion when prints are flattened or
mounted. Also, the avoidance of alum may reduce silver complexes bound
in the emulsion which can speed wash times.

If one wishes to remove hardener for toning, the following treatments may be
used: household ammonia diluted 1:10 (0.3%) for 2 min with 45 min wash or 5
min in 2% solution of Kodalk or sodium carbonate, then wash.

An exception to the rapid fix recomendation is Agfa Portriga paper which has
a soft emulsion. If it is sepia toned (basic toner removes hardeners),
emulsion damage may occur if the paper is heat dried. Therefore it should be
hardened after toning. If fibers from a canvas mat drier or blotters stick
to the emulsion, you may have that problem even with other papers. Kodak
makes a separate hardener, however, I find the hardener offered by Sprint to
be effective and economical. I also use it with their rapid fixer.


Common Fixer Tests:

Tests for fixer exhaustion which rely on precipitation of silver iodide
aren't sensitive enough to determine whether a fixer is in the "archival"
range or "commercial" range, and in some cases, whether the fixer is near
exhaustion. Relying on that type of test with one-bath fixation invites
future disaster.

Likewise, tests of wash water for fixer can't detect insoluble complexes
of fixer in the paper or unfixed silver halide in the emulsion. Sulfide or
selenium toner tests for silver in paper don't measure the insoluble
complex (I) or degradation complexes, nor does silver nitrate react with
those complexes. Some tests may be better than none and any warnings should
be heeded, but in this instance, they may give a false sense of security if
the results are false negatives.

Follow the tables given by Haist (above), and reduce capacities by 1/2 for
TMax and other high tech emulsions.


Hypo-clear and Eliminator:

Usually, the removal of fixer and its complexes from film is fairly
straightforward. With or without hypo-clear, the hypo and complexes diffuse
out of the emulsion with washing, and aren't tightly bound. The potassium
alum used as a hardener may complex small amounts of hypo and silver
complexes, but that doesn't seem to occur with chrome alum. However, chrome
alum isn't used in commercial products, and probably should be avoided for
environmental reasons and staining problems.

With papers, additional problems can arise due to the nature of the support.
Some of the hypo and complexes are adsorbed to the baryta layer, fixer
always penetrates the interstices between fibers of fiber-base papers, and
with prolonged fixing (over 15-30 minutes), hypo and complexes can enter
the fiber "cells", from which it is very difficult to remove. However, this
does not occur with reasonable fixing times of 5 to 10 minutes.

The hypoclearing properties of saline solutions was discovered by Dr. Bannow
in 1889, but he used a 10% sodium chloride solution (100,000 ppm) with
rinses with moderate success. In 1903, Dr. Bayssellanee found that sea
water was more effective, and used 30,000 ppm sea salt with 1 hour soaks
followed by washes to remove salt (so much for the "US Navy discovery"
myth).

Although it was noted that film and paper washed in sea water (3%
salts of which 2.6% is sodium chloride) lost fixer much more rapidly than
washing in tap water (65% faster for film; 80-90% faster for paper), using
table salt or sea salt as a clearing agent isn't a good idea. Removal of
chloride was required, since chloride resulted in faster degradation of any
residual hypo in the emulsion (note: the seawater use was for rapid
processing and conservation of fresh water, not archival stability).

Subsequently other hypo-clearing agents were examined, and polyvalent anions
were found to be most effective in displacing silver. Of the group, 2%
sodium sulfite buffered to pH 7.0 was found to be most effective. EDTA or
other chelating agents may be included to remove calcium sulfite which can
precipitate in/on emulsions.

Although some suppliers indicate that a short soak in hypo-clear (1 min)
after fixing followed by a short wash time is adequate, rinsing films and
papers before a 10 minute hypoclearing agent treatment works better, and
prolongs hypo-clear life.

Hypo-Eliminators

Hypo-eliminators rely on the use of an oxidant such as peroxide to
rapidly oxidize any residual hypo complexes in the film, preventing the
reaction with image silver which would occur if they were permitted to
degrade. Kodak HE-1 is a dilute mixture of peroxide and ammonia made up when
used (never kept in an enclosed container) which oxidizes such complexes.
However, it has been noted that oxidation is incomplete unless bromide is
added to speed the reactions.

In the "Craft of Photography" Vestal mentions that some studies indicated
that HE-1 treatment wasn't as "archival" as supposed, and that a small
amount of thiosulfate might stabilize the image. The point was clarified at
a subsequent conference reported by Vestal. The topic is considered below
(RC papers and stability).

The current concensus seems to indicate that hypo-eliminators should not be
used unless the image is subsequently toned with selenium or sulfur (sepia),
or treated with Agfa's Sistan (thiocyanate).


The Ilford Story:

Coinciding with the introduction of Galerie paper, Ilford decided to
introduce a quick 20 minute archival processing procedure. After development
and stop, paper was to be fixed for 30 seconds in film strength rapid fixer,
followed by a five minute wash, 10 minute soak in a wash aid, and another 5
minute wash.

Later, the recommended fixing time was extended to 1 minute with little
fanfare. If the wash aid isn't used, Ilford recommends a wash time of at
least one hour. The precautions mentioned include good agitation, and use of
fixer which hasn't approached its capacity. The "theory" is that silver
removal from the emulsion is faster than accumulation in paper interstices,
so supposedly little accumulation occurs.

There are some problems.

The procedure does _not_ work with Kodak papers and others which require
longer fixing times. (Elite is a prime example.)

Also, the retention of complex I in the paper isn't addressed or tested for,
and complete non-image silver removal isn't checked.

Ilford recommends one bath rapid fixation. A capacity of 40 sheets of
8x10 paper per qt (160 per gal) is suggested when a wash aid is used with a
single fixing bath or when a two bath system is used (which negates the
short fixing time rationale). However, the capacity is reduced to 10 sheets
per qt (40 per gal) using a regular wash and single bath fix.

That disparity in capacities suggests that Ilford is relying on the wash aid
to extend so-called fixer capacity when a single bath is used. The
implication is that for the 30 sheet difference between use and non-use of
wash aid, significant insoluble complexes are carried over (see the Haist
table). Note that Ilford's capacities for single bath fixing are greater
than Haist's recommendation for commercial processing (Ilford uses 2 g/l
with wash aid or 0.5 g/l without). Their rapid fix might have a slightly
greater capacity, but it is unlikely that silver levels are as low as
Haist's _archival_ standard when silver levels higher than Haist's limit for
commercial processing are tolerated.

In the current Ilford tech sheet on Galerie, they mention that the archival
treatment with a 20 min wash results in 1/4 the level of hypo in the paper
as a 5-10 minute fix with "normal" washing. Note that a wash aid wasn't used
with the paper fixed 5 to 10 minutes in the "comparison". Remember, wash
aids can increase rate of fixer removal by 80-90% with papers. The
comparison really isn't valid, and it appears that Ilford's only standard
for archival processing is residual reactive (free) hypo levels, and not the
target of absence of insoluble monoargentothiosulfate and silver halide.

Toning

I don't intend to cover this in any detail, other than to say that selenium
or sepia toning is required to ensure image permance, especially if prints
are displayed. Gelatin always retains some water which can dissolve
atomospheric oxidizing gases such as ozone and nitrous oxides, which can
bleach the image and permit silver migration.

Toning in selenium (1:3 for color chage to 1:20 for permance with minimal
tone effect), or sepia prevents the problem. Also, it is claimed that
treatment with Agfa's Sistan protects the image, though I can't find data to
support their contention.

There are a number of arcane approaches to selenium toning. If Rapid
Selenium Toner is exposed to hypo in an acidic environment (acid fixer), the
selenite will be reduced to colloidal or metallic selenium, and a red stain
will result. To avoid that problem, rinse the paper after fixing, and dilute
the Rapid Selenium Toner in a solution of 2% Kodalk (20 g/l) rather than
water or hypoclearing agent. The dilute toner may be stored in a glass
container until exhausted through use.


Water Spots

Water spots are caused by high salt or particulate concentrations in wash
water, which dry onto/in the emulsion. If you have problems with water
spots, then soak the negatives or RC prints in the following solution for a
few minutes before hanging to dry (don't use a squeegee - water will run off):

1 gal distilled water
10 ml Photoflo
100 ml 70% isopropanol (rubbing alcohol from a pharmacy - be sure that it
doesn't contain anything else)

The solution can be reused if it's filtered before returning it to the
storage container.

[Richard Knoppow]

"taco*boy" <se...@snet.net> wrote:

>Is fixer OK to use over and over and over? I've heard that fixer will turn
>purple when depleted. I have never seen this. Am I wasting fixer I throw it
>away and it's still clear?
>

>Thanks,
>
>Scott
>
>
Hypo can be used several times but has a limited capacity. It does
not change color. You are thinking of indicator stop bath. This has a
dye in it which is yellow as long as the stop bath is sufficiently
acid but becomes purple when it moves toward neutral. Under the usual
safe light it will appear to turn black when its reached its capacity.
The old rule of thumb for hypo is to measure the clearing time when
it is fresh and replace it when the clearing time doubles.
The clearing time is the time it takes a scrap of unprocessed film
to become clear when put into the bath; around two the three minutes
for most film in a standard fixing bath.
In fact, the bath really should be changed before this.
The fixing bath changes the undeveloped silver compounds in the
emulsion into a form which is water soluable so that they will wash
out. Some comes out in the fixing bath itself, much comes out in the
washing stage. The conversion requires a couple of stages of chemical
reactions. When the fixer reaches a certain point of exhaustion it
will no longer complete the reaction. Although it will still clear the
film so that it doesn't turn dark in the light, some of the silver
compounds are in a form which is not water soluable so they stay in
the film or paper. Eventually, they will cause a chemical reaction
with atmospheric gasses which will attack and destroy the metalllic
silver of which the image is made. The film or paper will slowly
develop a brown or yellow stain and some of the image will fade.
The best cure is not to overwork the fixer. One way of extending the
life of the fixing bath and insuring complete fixation is to use two
fixing baths and fixing for half the time in each. The first bath does
most of the fixing leaving the second one relatively fresh. The second
cleans up after the first one. Two baths have about four times the
capacity of a single bath.
For more details see the _Kodak Black-and-White Darkroom Dataguide_
available from camera shops with darkroom supply departments. This
book also has information on how to mix and use a fixing bath testing
solution.
---
Richard Knoppow
Los Angeles, Ca.
dick...@ix.netcom.com

[Darren Stehr]

Fix turns purple from all those nice "anti-" coatings incorporated into film
emulsions.
This in no way indicates whether it is good or bad.
See Knoppow's post for one way of testing fix

[Peter]

taco*boy wrote:
>
> Is fixer OK to use over and over and over? I've heard that fixer will turn
> purple when depleted. I have never seen this. Am I wasting fixer I throw it
> away and it's still clear?
>
> Thanks,
>
> Scott

You may be thinking of Indicator Stop Bath which turns a deep purple
when exhausted. Fixer will become useless after you've fixed a number
prints and negatives. You can test the fixer with Edwal Hypo Check, or
with some Kodak Silver Estimating Test Papers, which is a litmus paper
that indicates how much silver is in the fixer.
--
P.M.