Exausted fix for Paper.... Any simple test?

[Gerald C Koch]

IngMacca,

Your test is not adequate to determine if the paper has been fully fixed. Unfixed compounds in the paper will have a degrading effect much later...

And, despite what many say, the clip test isn't really adequate for paper, especially if you are processing fiber-base paper and trying to process for optimum permanence. The acceptable dissolved silver level in fixer for film is much higher than for paper processed for optimum permanence. The silver test strips also only start to indicate after a single fixing bath has reached or gone past its minimum level of dissolved silver for optimum permanence. They would, however be useful for two-bath fixing regimes, for film fixer and for processing to less than optimum permanence.

To answer your question then: There is really no "simple" and accurate way of determining fixer capacity for paper, particularly when processing for permanence. The whole issue of adequate fixing is more complicated, but worth learning about.

There are, however, a couple of methodologies that will ensure good fixing for paper without going to a lot of trouble.

The first is simply to keep track of the number of prints you put through your fixer and then follow the manufacturer's recommendations for throughput.

Unfortunately, there are a couple of different standards out there that confuse the issue. The less-stringent method often called "general purpose" or "for commercial use" or something similar, and assumes a less-than-maximum print lifespan. In other words, prints processed "for commercial use" are not processed for optimum permanence; that's a different standard. The capacity numbers given are often for "commercial" standards, not "archival" ones. We need to be sure that the capacity numbers we use are for the degree of permanence we desire.

I assume, since you are in Italy, that you are using Ilford or Tetenal products. I recommend highly that you get the Ilford tech sheet on Rapid Fixer and read it carefully, especially the sections on two-bath fixing and silver concentration. The document is here: http://www.ilfordphoto.com/Webfiles/2006130218312091.pdf

Note that Ilford's "commercial standard" is 40 8x10 prints per liter, but that that drops to 10 8x10 prints per liter for "optimum permanence." Here's the quote from the top of page 4, second column in the section on silver concentration: "For prints that need maximum stability for long term storage a the maximum silver level in
the fixer should not rise above 0.5 g/l i.e., approximately 10 20.3 x 25.4cm (8 x 10in) prints [per liter]."

If you fix using a single fixing bath, and wish your prints to last as long as possible, then stick to the 10 8x10s per liter capacity. Or, alternately, you can opt for two-bath fixing (which I use and recommend). With this method, you can use the first bath up to the 40 8x10s per liter (of bath one) since the relatively fresh second bath completes the fixing process. The process is described in the Ilford document.

If you wish to take the next step, it involves getting into process control a bit. The idea is to test your fixed and washed prints for residual silver (adequate fixing) and residual hypo (adequate washing). There are a couple of easy-to-make or find test solutions for this: ST-1 (Kodak's Silver Test 1) or selenium toner for determining safe levels of residual silver and HT-2 (Kodak's Hypo Test 2) for determining if the fixer has been adequately washed from the print. Using them is not all that complicated, but this post is long enough already. If you're interested, search here for more posts from me and others on the subject.

Best,

Doremus

+1

Why is it some many on APUG resist keeping track of the number of prints/films put through a fixing solution??? They all seem to want some sort of test. These tests are not particularly accurate and as stated more than once it is archival permanence that is desired. This is lost way before the fixing solution fails to clear a print. If you MUST test then check for retained silver in a sample print.

Just a general observation. This question has been asked a number of times. If those new to photography would invest in a good book on photographic processing such questions would not have to be asked. Even searching the APUG archives before posting would be helpful.

 

[miha]

Some years ago, in a conversation with Mirko of Fotoimpex, he told be that they had customers fixing for one year with the same bottle of fixer and then complaining about stains etc. They were abviously expecting for something to "happen" with the fixer...

 

[Doremus Scudder]

What we need is fixer that turns green, or explodes, or otherwise self-destructs when the dissolved silver level hits 0.5g/l ... or do we go with Haist's 0.2g/l ? But wait, film can tolerate up to 10g/l according to Ilford.... I guess I'll just have to keep counting and testing.

Humor aside, it's pretty easy to keep a tally of the number of prints (test strips included) that you put through the fix. I just make hash marks on my white board.

And the testing is pretty easy too. I did initial tests to find the limits of my workflow and now test either the last print through the fix/wash (usually it's the same one) or run a black test sheet as the last sheet through the fix after the capacity has been reached. My tests are now KRST 1+2 or even straight to test for retained silver and the Kodak HT-2 test to test washing. I might toss my fix a bit before it's really exhausted and my wash times may be longer than minimum needed, but my prints always pass the tests with flying colors.

Doremus

 

[Rudeofus]

When it comes to testing fixers for exhaustion, a number of issues exist, which make such tests exceedingly difficult:

1. Not all silver salts are created equal. Silver Chloride is quite soluble even in exhausted fixer, whereas Silver Iodide is very hard to fix. Therefore fixer exhaustion also depends on what kind of photographic product is to be fixed or has been fixed before.
2. Fixation is not just a competition between silver halides and soluble silver thiosulfate complexes, there are many intermediate compounds with wildly varying solubility. It also depends on whether Potassium, Sodium or Ammonium ions are present, and their presence may change as developer or other photographic bathes are carried over. Sodium Thiosulfate fixers can dissolve much smaller amounts of Silver Iodide than Ammonium Thiosulfate based ones even if their molar concentration is the same.
3. Photographic developers can also bring restrainers into the fixer through carry over, some of which stick to silver ions. These restrainers can either slow down fixation by preventing fixing compounds from reaching silver ions, and they can form competitive insoluble silver salts.
4. The amount of silver halide, which can be dissolved by fixer, is strongly dependent on fixer concentration, and fixer concentration will change as water is carried over. Therefore even an accurate assessment of silver concentration may not tell much about exhaustion.
5. As fixers approach exhaustion, they will leave poorly soluble intermediate compounds behind, typically some mixed salts of silver, alkali, thiosulfate and halide. Some of these mixed compounds will eventually wash out, but much, much slower than soluble silver thiosulfate complexes. It therefore also depends on washing procedure, whether a fixer can reach archival silver levels.

For all these reasons listed above, it is much better to test archival fixation in the film/paper, not in the fixer. These test solutions can be made very cheaply, and last a long time.

 

[Gerald C Koch]

When it comes to testing fixers for exhaustion, a number of issues exist, which make such tests exceedingly difficult:

1. Not all silver salts are created equal. Silver Chloride is quite soluble even in exhausted fixer, whereas Silver Iodide is very hard to fix. Therefore fixer exhaustion also depends on what kind of photographic product is to be fixed or has been fixed before.
2. Fixation is not just a competition between silver halides and soluble silver thiosulfate complexes, there are many intermediate compounds with wildly varying solubility. It also depends on whether Potassium, Sodium or Ammonium ions are present, and their presence may change as developer or other photographic bathes are carried over. Sodium Thiosulfate fixers can dissolve much smaller amounts of Silver Iodide than Ammonium Thiosulfate based ones even if their molar concentration is the same.
3. Photographic developers can also bring restrainers into the fixer through carry over, some of which stick to silver ions. These restrainers can either slow down fixation by preventing fixing compounds from reaching silver ions, and they can form competitive insoluble silver salts.
4. The amount of silver halide, which can be dissolved by fixer, is strongly dependent on fixer concentration, and fixer concentration will change as water is carried over. Therefore even an accurate assessment of silver concentration may not tell much about exhaustion.
5. As fixers approach exhaustion, they will leave poorly soluble intermediate compounds behind, typically some mixed salts of silver, alkali, thiosulfate and halide. Some of these mixed compounds will eventually wash out, but much, much slower than soluble silver thiosulfate complexes. It therefore also depends on washing procedure, whether a fixer can reach archival silver levels.

For all these reasons listed above, it is much better to test archival fixation in the film/paper, not in the fixer. These test solutions can be made very cheaply, and last a long time.

Very well said. Now if people can realize that it is the print that needs to be tested and not the fixing solution progress will be made.

 

[RalphLambrecht]

The silver estimating papers are a good way to go, the various iodide based "hypo" check solutions will only tell you that your fixer is already bad, sort of a post crash "collision alert". I simply use a tally mark for each 8x10 print on my fixer bottle. I use two fixers for fiber base and one for RC papers. For RC I use the same first fixer that is part of my two bath fixer system. Capacity is 20-25 8x10's per quart, I make that as 100 prints for a gallon. When the first fixer reaches that mark I promote the second bath to first fixer and mix a new second fixer bath. I first make tally marks on a piece of scrap paper, in columns for the different sizes and then at the end of the day, transfer the marks to the jug.

I believe this is a good way to go

 

[miha]

1. As fixers approach exhaustion, they will leave poorly soluble intermediate compounds behind, typically some mixed salts of silver, alkali, thiosulfate and halide. Some of these mixed compounds will eventually wash out, but much, much slower than soluble silver thiosulfate complexes. It therefore also depends on washing procedure, whether a fixer can reach archival silver levels.

Above might be the reason behind the Principle of good fixation guidance by Ilford: #3 Use a single fixing bath plus a washing aid. The number of prints through the single fixing bath can be increased to approximately 40 20. 3x25. 4cm (8x10 inch) prints per litre/US quart of working strength fixer.