Chuck,
My views have evolved since the original post in 2002
You need to know that the "minimal fixing time" regime developed by Ilford relies on fixing times of 60 seconds (or less) with a strong-enough (i.e., "film-strength") fixer to do the fixing job before the fixer has time to completely soak into the base of the fiber-base paper. This keeps fixer by-products from adhering to the paper fibers, which makes the paper easier to wash.
Fixing times longer than 60-seconds allow fixer to saturate the paper base and, therefore, washing time needs to be longer (and a wash aid, such as Hypo Clearing Agent, is indispensable).
So, there are a few strategies to achieving an "archival" level of fixation. Which one you choose depends on the time-vs-economy aspects and other practical considerations (e.g., print draining time, etc.).
!. Ilford's quick-fix method. Use fresh film-strength fixer and fix for 60 seconds total - no longer - following the method outlined on Ilford's website here: https://www.ilfordphoto.com/ilford-optimum-permanance-wash-sequence-fb-papers/ . That would be Ilford Rapid Fixer or Hypam at a 1+4 dilution or Kodak Rapid Fixer at the 1+3 dilution.
Note the five-minute running water rinse right after fixing and that the wash-aid step is long; these are both indispensable parts of the sequence, which relies on the rinse to remove much of the fixer to start and the wash-aid to provide a great deal of the washing function. Note also that to achieve the optimum level of fixation, your fixer capacity will be approximately 10 8x10-inch prints per liter of fixer. After that, the dissolved silver level is too high for what Ilford regards as "maximum stability." All this, of course, assumes a single-bath fixation. Note also that Ilford does not like silver test strips. And note too that if you tone your prints, the final wash is significantly longer.
Ilford's tech sheet has all the info. Here are the relevant paragraphs (emphasis mine):
"If a high level of image permanence is required
for commercial use the silver concentration in the
fixer should be kept below 2 g/l when fixing FB
papers. This approximates to 40, 20.3 x 25.4
cm, (8 x 10 inch) FB prints. Above this level
compounds may remain in the paper base after
washing and over time possibly contribute to print
staining. 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.
However, print throughput can only be a guide to
silver concentration as it depends on the
proportion of exposed to unexposed areas on the
prints being processed. Silver estimator papers are
usually not sensitive enough to test the very low
silver levels suitable for optimum permanence. For
important prints it is recommended that paper is
tested in the following way to ensure adequate
fixing..."
Ilford goes on at this point to recommend the Kodak ST-1 test to test for residual silver. A viable alternative to the ST-1 test is to use Kodak Rapid Selenium Toner (I expect other toners would work too), diluted 1+9 or stronger instead. The testing method is the same.
Two-bath variation of the above to increase fixer capacity and economy: Mix two fixing baths and then divide the total fixing time between the two. Note you still need to keep total fixing time under 60 seconds, so you need to include print drain time in the total time as well. That might mean something like: immerse print in bath one, agitate for 20 seconds, drain print for 10 seconds, transfer to bath two, agitate for 20 seconds, drain for 10 seconds and transfer immediately to a running-water rinse.
With two-bath fixation, you can effectively double the throughput capacity of your fixer (or more, with promotion of bath two to bath one) to 20 8x10-inch prints per liter. Say you have two one-liter fixing baths (two liters total). You can run approx. 40 8x10-inch prints though bath one and bath two and achieve the same level of permanence, since bath two stays fresh, with little dissolved silver, and finishes off the fixing begun in bath one.
After throughput capacity for the first bath has been reached, you can discard it and replace it with bath two, since bath two is still really fresh. Then you mix a new second bath and begin again, with the same throughput capacity numbers. This promotion step can be repeated several times (I don't like more than four, but I believe Kodak says six or seven) until both baths need to be mixed fresh.
2. Fixing for longer with "paper-strength" fixer. For decades, Kodak and others recommended a longer fixing time for fiber-base papers with a weaker dilution of rapid fixer. This would equate to Ilford's 1+9 dilution for their products and Kodak's 1+7 dilution for its Rapid Fixer. This method requires more wash time than Ilford's "short-fix" method.
Here there are some discrepancies on recommended times. Ilford gives two minutes for fixing fiber-base prints in Rapid Fixer 1+9. Note, however, that this is the "average minimum fixing time at 20ºC (68ºF) for materials manually processed using fresh fixer." They don't tell you fixing times for fixer near the point of exhaustion. Kodak isn't much more help with their recommendation of "2:30 - 5 minutes" for two-bath fixation or "10 minutes" for single-bath fixation. These are basically the same times Kodak gives for non-rapid, "conventional" sodium-thiosulfate-based fixers.
In any case, I think here is where you need to do your own testing to find a practical fixing time for which ever regime you choose to use, one or two-bath. Kodak's times, as noted above, are likely predicated on using the optional hardener for Rapid Fix, which slows fixation and extends wash time. Not using the hardener (recommended) should result in times close to that Ilford lists.
I have found that, for my two-bath regime, 2 - 2.5 minutes in a non-hardening "paper strength" rapid fixer does the job well with a throughput capacity of approx. 40 8x10s per liter (I like 36, actually, since it is exactly three washer loads for me). I test the last print through every printing session using the selenium-toner test for residual silver. Do your own testing, however.
Note that extending fixing time a bit really makes no difference. After the paper base has become saturated, you will need extended washing (more later) and "overfixing," i.e., bleaching of print highlights isn't really an issue until much longer than 10 minutes total in the fix (otherwise, Kodak likely would not have recommended 10 minutes...).
You can use a single-bath regime with "paper-strength" fixer as well, but the same capacity constraints apply: you're limited to 10 8x10s per liter if you want optimum permanence. Plus, with the weaker fix, you run a greater risk of underfixing. I recommend two-bath fixation here.
Notes on washing:
Ilford has found that the longer treatment in a wash aid really helps remove fixer by-products better than shorter times. They recommend a five-minute running water rinse, followed by 10 minutes in Wash Aid and either a five-minute final wash or, if a selenium toner step was added, a 30-minute final wash in running water.
Kodak still recommends a one-minute running water rinse, followed by three minutes in Hypo Clearing Agent and the a 20-minute wash for fiber-base prints. They don't seem to take toning into account at all.
In my workflow, I opt for the more thorough Ilford approach, but often extend that. My final wash is usually 60 minutes. Testing for residual hypo is good here too (a different test than residual silver!). My prints always pass with flying colors.
Here's a link to Kodak's Rapid Fix instructions: https://www.freestylephoto.com/static/pdf/product_pdf/kodak/KODAK_RAPID_FIXER_INSTRUCTIONS.pdf
And Ilford's Rapid Fixer tech sheet: https://www.freestylephoto.com/pdf/product_pdfs/ilford/IlfordRapidFixer.pdf
Hope all this helps,
Doremus
My views have evolved since the original post in 2002
You need to know that the "minimal fixing time" regime developed by Ilford relies on fixing times of 60 seconds (or less) with a strong-enough (i.e., "film-strength") fixer to do the fixing job before the fixer has time to completely soak into the base of the fiber-base paper. This keeps fixer by-products from adhering to the paper fibers, which makes the paper easier to wash.
Fixing times longer than 60-seconds allow fixer to saturate the paper base and, therefore, washing time needs to be longer (and a wash aid, such as Hypo Clearing Agent, is indispensable).
So, there are a few strategies to achieving an "archival" level of fixation. Which one you choose depends on the time-vs-economy aspects and other practical considerations (e.g., print draining time, etc.).
!. Ilford's quick-fix method. Use fresh film-strength fixer and fix for 60 seconds total - no longer - following the method outlined on Ilford's website here: https://www.ilfordphoto.com/ilford-optimum-permanance-wash-sequence-fb-papers/ . That would be Ilford Rapid Fixer or Hypam at a 1+4 dilution or Kodak Rapid Fixer at the 1+3 dilution.
Note the five-minute running water rinse right after fixing and that the wash-aid step is long; these are both indispensable parts of the sequence, which relies on the rinse to remove much of the fixer to start and the wash-aid to provide a great deal of the washing function. Note also that to achieve the optimum level of fixation, your fixer capacity will be approximately 10 8x10-inch prints per liter of fixer. After that, the dissolved silver level is too high for what Ilford regards as "maximum stability." All this, of course, assumes a single-bath fixation. Note also that Ilford does not like silver test strips. And note too that if you tone your prints, the final wash is significantly longer.
Ilford's tech sheet has all the info. Here are the relevant paragraphs (emphasis mine):
"If a high level of image permanence is required
for commercial use the silver concentration in the
fixer should be kept below 2 g/l when fixing FB
papers. This approximates to 40, 20.3 x 25.4
cm, (8 x 10 inch) FB prints. Above this level
compounds may remain in the paper base after
washing and over time possibly contribute to print
staining. 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.
However, print throughput can only be a guide to
silver concentration as it depends on the
proportion of exposed to unexposed areas on the
prints being processed. Silver estimator papers are
usually not sensitive enough to test the very low
silver levels suitable for optimum permanence. For
important prints it is recommended that paper is
tested in the following way to ensure adequate
fixing..."
Ilford goes on at this point to recommend the Kodak ST-1 test to test for residual silver. A viable alternative to the ST-1 test is to use Kodak Rapid Selenium Toner (I expect other toners would work too), diluted 1+9 or stronger instead. The testing method is the same.
Two-bath variation of the above to increase fixer capacity and economy: Mix two fixing baths and then divide the total fixing time between the two. Note you still need to keep total fixing time under 60 seconds, so you need to include print drain time in the total time as well. That might mean something like: immerse print in bath one, agitate for 20 seconds, drain print for 10 seconds, transfer to bath two, agitate for 20 seconds, drain for 10 seconds and transfer immediately to a running-water rinse.
With two-bath fixation, you can effectively double the throughput capacity of your fixer (or more, with promotion of bath two to bath one) to 20 8x10-inch prints per liter. Say you have two one-liter fixing baths (two liters total). You can run approx. 40 8x10-inch prints though bath one and bath two and achieve the same level of permanence, since bath two stays fresh, with little dissolved silver, and finishes off the fixing begun in bath one.
After throughput capacity for the first bath has been reached, you can discard it and replace it with bath two, since bath two is still really fresh. Then you mix a new second bath and begin again, with the same throughput capacity numbers. This promotion step can be repeated several times (I don't like more than four, but I believe Kodak says six or seven) until both baths need to be mixed fresh.
2. Fixing for longer with "paper-strength" fixer. For decades, Kodak and others recommended a longer fixing time for fiber-base papers with a weaker dilution of rapid fixer. This would equate to Ilford's 1+9 dilution for their products and Kodak's 1+7 dilution for its Rapid Fixer. This method requires more wash time than Ilford's "short-fix" method.
Here there are some discrepancies on recommended times. Ilford gives two minutes for fixing fiber-base prints in Rapid Fixer 1+9. Note, however, that this is the "average minimum fixing time at 20ºC (68ºF) for materials manually processed using fresh fixer." They don't tell you fixing times for fixer near the point of exhaustion. Kodak isn't much more help with their recommendation of "2:30 - 5 minutes" for two-bath fixation or "10 minutes" for single-bath fixation. These are basically the same times Kodak gives for non-rapid, "conventional" sodium-thiosulfate-based fixers.
In any case, I think here is where you need to do your own testing to find a practical fixing time for which ever regime you choose to use, one or two-bath. Kodak's times, as noted above, are likely predicated on using the optional hardener for Rapid Fix, which slows fixation and extends wash time. Not using the hardener (recommended) should result in times close to that Ilford lists.
I have found that, for my two-bath regime, 2 - 2.5 minutes in a non-hardening "paper strength" rapid fixer does the job well with a throughput capacity of approx. 40 8x10s per liter (I like 36, actually, since it is exactly three washer loads for me). I test the last print through every printing session using the selenium-toner test for residual silver. Do your own testing, however.
Note that extending fixing time a bit really makes no difference. After the paper base has become saturated, you will need extended washing (more later) and "overfixing," i.e., bleaching of print highlights isn't really an issue until much longer than 10 minutes total in the fix (otherwise, Kodak likely would not have recommended 10 minutes...).
You can use a single-bath regime with "paper-strength" fixer as well, but the same capacity constraints apply: you're limited to 10 8x10s per liter if you want optimum permanence. Plus, with the weaker fix, you run a greater risk of underfixing. I recommend two-bath fixation here.
Notes on washing:
Ilford has found that the longer treatment in a wash aid really helps remove fixer by-products better than shorter times. They recommend a five-minute running water rinse, followed by 10 minutes in Wash Aid and either a five-minute final wash or, if a selenium toner step was added, a 30-minute final wash in running water.
Kodak still recommends a one-minute running water rinse, followed by three minutes in Hypo Clearing Agent and the a 20-minute wash for fiber-base prints. They don't seem to take toning into account at all.
In my workflow, I opt for the more thorough Ilford approach, but often extend that. My final wash is usually 60 minutes. Testing for residual hypo is good here too (a different test than residual silver!). My prints always pass with flying colors.
Here's a link to Kodak's Rapid Fix instructions: https://www.freestylephoto.com/static/pdf/product_pdf/kodak/KODAK_RAPID_FIXER_INSTRUCTIONS.pdf
And Ilford's Rapid Fixer tech sheet: https://www.freestylephoto.com/pdf/product_pdfs/ilford/IlfordRapidFixer.pdf
Hope all this helps,
Doremus
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