Monster Fixer Experiments

Paul Verizzo · Jun 27, 2022

Fourteen years ago I was doing lots of photography and was extremely active on this forum. I went down a rabbit hole......well, OK, many of them....about fixers. After a photo hiatus of the last eight years, I'm getting back into the game. I am re-reading things here and materials I wrote and kept.

One of those matters to be reviewed was the dozens of experiments I did on fixers. If you enjoy the chemistry quest, you will be amazed at what I discovered.

Good ole APUG (Photrio will always be APUG to me.) My PDF is still online.

https://www.photrio.com/forum/attachments/fixer-experiments-narrative-pdf.6105/

Helge · Jun 28, 2022

Personally I don’t care too much about time and cost.

The most important thing to me is archivability and if there’s possibly a tiny tiny affect/difference an image quality.

When developing, those extra few minutes mean very little to me, if it compromises the above factors.

Did any of your experiments address those aspects?

Rudeofus · Jun 28, 2022

Very nice writeup!

Allow me to add a few comments:

I tested 300 grams/liter of hypo and got a time reduced from #4 to a time to clear of 35 seconds. Relatively linear. Now I started adding ammonium sulfate, one gram at a time.

You will notice, that at 200 g/l hypo you can add more ammonium salt to get optimal fixing speed. My favorite combo was Ammonium Acetate, which I got by adding equal amounts of Ammonia 24% and Acetic Acid 80% solution. The mixing of these two heated up the water such that dissolution of hypo was much faster. The fixing speed with Ammonium Acetate is much better than with Ammonium Chloride.

Hypo at 300 g/l with 70 grams ammonium sulfate kicks ass, but gets its ass kicked by plain old ammonium thiosulfate.

The biggest drawback of hypo is not its slower fixing speed, but its much reduced capacity. There are insoluble mixed salts of sodium, silver, halide and thiosulfate, which can bring fixation speed to a crawl. These will not be an issue with fresh fixer, but only as silver and halide levels build up in used fixer. This may also explain the very long fixer times specified for commercial hypo fixers.

I don’t develop or print as much as I wish I would, so fixer cost is not a budget consideration.

If one doesn't process a lot of material, longevity of fixer is a concern. This will be much improved with neutral or alkaline fixer. Alkaline rapid fixer tends to release smelly Ammonia, therefore neutral fixer is the best here IMHO.

my aversion to shipping water loses out to the increased efficiency of ammonium thiosulphate

I once ran the numbers, and the amount of water shipped with Ammonium Thiosulfate 60% solution is equivalent to the amount of water shipped with Sodium Thiosulfate Pentahydrate. Yes, sometime the water is hard to see, but it's always there and always heavy.

Capacity: I would like to think that a general conclusion could be reached by the number of thiosulfate molecules in a given compound.

Capacity depends on number of thiosulfate molecules, on counter anion (ammonium better than sodium better than potassium). The strangest counter anion is potassium, since potassium hypo is actually faster than sodium hypo, but its capacity is even worse due to these mixed salts forming after some use. Oh, and don't forget the type of halide used in different films!

Paul Verizzo · Jun 28, 2022

Helge said:
Personally I don’t care too much about time and cost.

The most important thing to me is archivability and if there’s possibly a tiny tiny affect/difference an image quality.

When developing, those extra few minutes mean very little to me, if it compromises the above factors.

Did any of your experiments address those aspects?

If you read it, no.

Archivability has a lot to do with washing. Not fixing. Adequate time, it doesn't matter what fixer is used.

Paul Verizzo · Jun 28, 2022

Rudeofus said:
Very nice writeup!

Allow me to add a few comments:

You will notice, that at 200 g/l hypo you can add more ammonium salt to get optimal fixing speed. My favorite combo was Ammonium Acetate, which I got by adding equal amounts of Ammonia 24% and Acetic Acid 80% solution. The mixing of these two heated up the water such that dissolution of hypo was much faster. The fixing speed with Ammonium Acetate is much better than with Ammonium Chloride.

The biggest drawback of hypo is not its slower fixing speed, but its much reduced capacity. There are insoluble mixed salts of sodium, silver, halide and thiosulfate, which can bring fixation speed to a crawl. These will not be an issue with fresh fixer, but only as silver and halide levels build up in used fixer. This may also explain the very long fixer times specified for commercial hypo fixers.

If one doesn't process a lot of material, longevity of fixer is a concern. This will be much improved with neutral or alkaline fixer. Alkaline rapid fixer tends to release smelly Ammonia, therefore neutral fixer is the best here IMHO.

I once ran the numbers, and the amount of water shipped with Ammonium Thiosulfate 60% solution is equivalent to the amount of water shipped with Sodium Thiosulfate Pentahydrate. Yes, sometime the water is hard to see, but it's always there and always heavy.

Capacity depends on number of thiosulfate molecules, on counter anion (ammonium better than sodium better than potassium). The strangest counter anion is potassium, since potassium hypo is actually faster than sodium hypo, but its capacity is even worse due to these mixed salts forming after some use. Oh, and don't forget the type of halide used in different films!

Thanks for those thoughts! I learned some things.

Helge · Jun 28, 2022

Paul Verizzo said:
If you read it, no.

Archivability has a lot to do with washing. Not fixing. Adequate time, it doesn't matter what fixer is used.

Efficient, complete and at the same time not over-fixing has implications on archivability.

Paul Verizzo · Jun 28, 2022

Not going to argue with you. Have a nice day.

Bill Burk · Jun 29, 2022

It was fun reading.

I have found fixer taking much longer than you report, with TMY2.

My typical Kodak Rapid Fixer dilution is 4 ounces plus 28 ounces to make a quart that fills the tank.

It’s probably because I go past the optimum dilution but your write-up gives me hope that time is the only cost when I mix this way.

I like having a convenient mix to remember, that doesn’t go through a bottle too quick.

A few times I caught my fixer taking too long to clear, when it got “overdiluted” by splash from the incoming water faucet.

But since I always use it fresh, I don’t have to worry about capacity.

Doremus Scudder · Jun 29, 2022

Some comments/observations:

Clearing time in fresh, unused fixer is going to be quite fast. As fixing by-products accumulate in the fixer with use, that time slows, but the fixer is still doing its job (i.e., completely converting the silver halides into water-soluble compounds). After a certain point, the concentration of silver and other by-products in the fixer is so great that the fixer no longer converts the halides into water-soluble compounds. Sometime before this happens, the fixer needs to be discarded.

The upshot of this is twofold: First, fixer exhaustion should be determined by the amount of dissolved silver in the fixer, not the number of thiosulfate molecules or whatever. In addition, levels of bromide and iodide inhibit fixer activity. The fixer capacity for bromide papers is less than that for chloride papers. T-Max and Delta films, with their higher iodide content need twice as much fixing time and reduce fixer capacity by 50% compared to "conventional" films due to the inhibiting influence of the iodide. Fixer dilution, therefore, plays little to no role in determining the working life of a fixer.

In addition to this, some materials can tolerate more dissolved silver in the fix and still be fixed adequately. Film and RC paper can deal with more silver in the solution than fiber-base paper. Therefore, what's being fixed plays a significant role in the determination of fixer capacity. Add to that the "degree" of fixing needed or desired and capacity numbers can change even more. There are different levels of fixation for fiber-base paper in particular, generally referred to as standards for "commercial use" or for "optimum permanence," etc.

Also, when using a fixer to treat as much film/paper as possible in a given volume, fixing times need to be based on the time the nearly-exhausted fixer needs to do the job, not the clearing time in fresh, unused fixer. Certainly, we could test and come up with a time for the initial batch of film or paper through the fix, and then test for times for subsequent batches, but that seems overly precise and much more trouble than it's worth. Finding a time or time range that works well for the fixer at the end of its useful life seems much more convenient, all other things being equal. The longer times given by manufacturers represent this.

And, while the test for clearing time is a useful guide for when to discard film fixer, it is less useful for determining fixing times. Yes, you test your fix, find 2x the clearing time and then fix your next roll of film for that time and pretty much be assured that the film is fixed adequately. However, if you do a test for clearing time for a liter of fix, double that, and then fix the next 15 rolls of film in that fix for that time, you're almost certainly going to underfix the last several rolls. Batch size and how close the fixer is to exhaustion play an important role here. Furthermore, while doubling clearing time should contain a certain safety factor (although I don't know this for sure, I've never tested how much past "clearing time" is needed for adequate film fixation) it's still a "minimum" time. Extending fixing time for everything but fiber-base papers has almost no disadvantage and can provide a welcome safety buffer. M. Gudzinowicz in his paper, "Post Development Processing," recommends for films either twice the clearing time in two fixing baths or simply using an extended fixing time of 5 minutes in each of two baths in order to "avoid problems and provide some security." This, for conventional films, rapid fixer, and a two-bath fixing regime!

Fixing fiber-base papers for optimum permanence is another can of worms entirely. Two-bath fixation and being sure to use the fixer to less than capacity is really the best insurance here. Even the good old tests for residual silver won't detect some retained by-products (Gudzinowicz again). Skimping on time and/or overusing fixer for this is simply not wise and a quest for fixer speed, to me at least, seems counter-productive. I'll leave the Ilford archival sequence for paper vs. longer fixing and washing times discussion for another thread

Best,

Doremus

Paul Verizzo · Jun 29, 2022

Doremus Scudder said:
Some comments/observations:

Clearing time in fresh, unused fixer is going to be quite fast. As fixing by-products accumulate in the fixer with use, that time slows, but the fixer is still doing its job (i.e., completely converting the silver halides into water-soluble compounds). After a certain point, the concentration of silver and other by-products in the fixer is so great that the fixer no longer converts the halides into water-soluble compounds. Sometime before this happens, the fixer needs to be discarded.

The upshot of this is twofold: First, fixer exhaustion should be determined by the amount of dissolved silver in the fixer, not the number of thiosulfate molecules or whatever. In addition, levels of bromide and iodide inhibit fixer activity. The fixer capacity for bromide papers is less than that for chloride papers. T-Max and Delta films, with their higher iodide content need twice as much fixing time and reduce fixer capacity by 50% compared to "conventional" films due to the inhibiting influence of the iodide. Fixer dilution, therefore, plays little to no role in determining the working life of a fixer.

In addition to this, some materials can tolerate more dissolved silver in the fix and still be fixed adequately. Film and RC paper can deal with more silver in the solution than fiber-base paper. Therefore, what's being fixed plays a significant role in the determination of fixer capacity. Add to that the "degree" of fixing needed or desired and capacity numbers can change even more. There are different levels of fixation for fiber-base paper in particular, generally referred to as standards for "commercial use" or for "optimum permanence," etc.

Also, when using a fixer to treat as much film/paper as possible in a given volume, fixing times need to be based on the time the nearly-exhausted fixer needs to do the job, not the clearing time in fresh, unused fixer. Certainly, we could test and come up with a time for the initial batch of film or paper through the fix, and then test for times for subsequent batches, but that seems overly precise and much more trouble than it's worth. Finding a time or time range that works well for the fixer at the end of its useful life seems much more convenient, all other things being equal. The longer times given by manufacturers represent this.

And, while the test for clearing time is a useful guide for when to discard film fixer, it is less useful for determining fixing times. Yes, you test your fix, find 2x the clearing time and then fix your next roll of film for that time and pretty much be assured that the film is fixed adequately. However, if you do a test for clearing time for a liter of fix, double that, and then fix the next 15 rolls of film in that fix for that time, you're almost certainly going to underfix the last several rolls. Batch size and how close the fixer is to exhaustion play an important role here. Furthermore, while doubling clearing time should contain a certain safety factor (although I don't know this for sure, I've never tested how much past "clearing time" is needed for adequate film fixation) it's still a "minimum" time. Extending fixing time for everything but fiber-base papers has almost no disadvantage and can provide a welcome safety buffer. M. Gudzinowicz in his paper, "Post Development Processing," recommends for films either twice the clearing time in two fixing baths or simply using an extended fixing time of 5 minutes in each of two baths in order to "avoid problems and provide some security." This, for conventional films, rapid fixer, and a two-bath fixing regime!

Fixing fiber-base papers for optimum permanence is another can of worms entirely. Two-bath fixation and being sure to use the fixer to less than capacity is really the best insurance here. Even the good old tests for residual silver won't detect some retained by-products (Gudzinowicz again). Skimping on time and/or overusing fixer for this is simply not wise and a quest for fixer speed, to me at least, seems counter-productive. I'll leave the Ilford archival sequence for paper vs. longer fixing and washing times discussion for another thread

Best,

Doremus

Good information, for sure. Outside of the scope of my original inquiry.

Monster Fixer Experiments

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