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Why two step fixing is a Really Good Thing

Dan Schwartz , Mar 08, 2004; 11:27 a.m.

Subject: Why two step fixing is a Good Thing

While looking at the thread entitled Again a purple tri-x question

I was led to an interesting article about two stage fixing ...And I Highly Recommend reading it.


 "taco*boy" <ses_2@snet.net> wrote: >Is fixer 
OK to use over and over and over? I've heard that> fixer will turn 
fixer  purple  when depleted. I have never seen this. >Am I 
wasting fixer I throw it away and it's still clear? 
 
The best option is to use  two  fixer 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 ocurs, 
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 fixer bath is fairly wasteful, 
though effective. 
 
Rather than using one fixer 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 fixer 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 fixer Bath  Fixation:
 
Grant Haist, the former director of research at Kodak, cites the 
following maximal permissible values for one-fixerbath   film and 
paper fixers for commercial and archival processing:  
 
One-fixer 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-fixer 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 
fixer bath  .
 
 
Two bath fixation:      Commercial      Archival
 
Film:
 
fixer Bath   1:
Max. Ag conc.:          6 g/l           3.5 g/l
Max. rolls/gal:         60-70           40
 
fixer 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:
 
fixer Bath   1:
Max. Ag conc.:           2 g/l            0.8 g/l
Max. sheets/gal:         200 8x10         70 8x10
 
fixer 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 fixer bath is used for the maximum number of sheets or 
rolls indicated, and then discarded after silver recovery. 
 
The second fixer 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 fixer two baths to that for 
one.     Two      bath   fixation is far more economical than using 
one fixer 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 fixer  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 fixer bath, rinsed and held in 
water, then fixed in the second fixer 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 fixer two  baths. The RC time 
is optimistic, though five minutes per fixer 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 fixer 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 fixer bath   1 of a fixer  two   fixer 
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 fixer 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-fixer 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 fixer 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 fixer bath   or when a fixer  two   
fixer 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 fixer bath   fix. 

That disparity in capacities suggests that Ilford is relying on the 
wash aid to extend so-called fixer capacity when a single fixer 
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 fixer 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.

Responses


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Lex Jenkins , Mar 08, 2004; 12:50 p.m.

Thanks, Dan. Interesting stuff.

Hans Beckert , Mar 08, 2004; 03:44 p.m.

I really do believe rapid fixer 3-5 minutes, with hardener, is all that need be done.

Chris Waller , Mar 09, 2004; 06:14 a.m.

Thanks for that, Dan. It's a very comprehensive explanantion of the chemistry. Very informative.

Bob Haight , Mar 09, 2004; 09:53 a.m.

I know Ilford reccommends a two stop bath for archival. I lean towards less use of the same fix, maybe, twice or so as opposed to two step fixing just to simplify things.

Dan Schwartz , Mar 09, 2004; 09:18 p.m.

Chris,

You mean two stage fixing, not two stage stop bath...

Hans,

That's the whole point of the article: You have to **assure** that the fixer removed the monoargentomonothiosulate (one silver cation and one hypo anion): Two stage fixing **assures** the halide and monoargentomonothiosulate removal.

The key point is that "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."

Cheers! Dan

Chris Waller , Mar 13, 2004; 05:02 a.m.

Dan,

It was Bob who mentioned two stop baths. Notwithstanding, having read that article yet again I shall adopt two-stage fixing for all future work.

Curt Sampson , Feb 20, 2005; 09:54 a.m.

Ctein, in his book Post Exposure, found that Sistan does work as well as toning for image protection on RC paper, at least in the short term (a few years under bright light). See page 160.

Noelle Kreeger , Jul 24, 2007; 04:08 p.m.

How would two-step fixing apply to single use chemistry and processing in a Jobo? Just put another dose of fixer in the tank after the first fixer bath? That would bring the total steps to nine with three done outside the machine.

Noelle Kreeger , Jul 25, 2007; 11:18 a.m.

Also, taco boy mentioned something about the 'clearing' of film. Is this when the film is no longer light-sensitive?


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