Quote Originally Posted by Rafal Lukawiecki View Post
... Doremus, you make good points about your process, ... I hope you will not be offended, however, if I politely question two points, ...

Ilford states: "Use a single fixing bath plus a washing aid. The number of prints through the single fixing bath can be increased to approximately 40 8x10" prints per litre working solution." in this document, page 3, right-hand column, point 3. This is in contrast to what they say is the capacity without a wash aid: "Fix only a few prints before replacing the fixing bath (approximately 10 8x10 inches prints). Similarly, this publication of Digital Truth, which is very similar to Ryuji Suzuki's findings, and on the Pure Silver mailing list. That document states: "Note that the processing capacity of fixer is considerably lower if fiber prints are processed without using a washing aid" and the capacity numbers show between twice and four times larger capacities of the fixer when a wash aid is part of the process." ...
Rafal,

Richard is correct about the commercial vs. "archival" standards. I'm not sure why Ilford says that a wash-aid will increase fixing capacity; I've really never seen convincing evidence that it can. What it can do, however, is help wash out compounds that might discolor more quickly. Take a look at this document
http://www.ilfordphoto.com/Webfiles/...0218312091.pdf and look at the section on silver concentration starting on pg. 4 bottom left. That should explain everything.

Personally, I think the information about fixers and capacities is more confusing than necessary and that the manufacturers are partly to blame for disseminating ambiguous and sometimes erroneous information. A wash-aid is largely sodium sulfite with a bit of buffering; it is not a fixer, will not change insoluble compounds to soluble and really cannot, therefore, increase fixer capacity as far as I can see. If someone has evidence to the contrary, I'd really like to see it... I don't seem to be able to find Ryuji Suzuki's document to read (which I would like to...). However, I do know that much of his research has been questioned by others on this forum much more knowledgeable than I, so I might tend to take his findings with a grain of salt till I saw some peer review. There may be a way that the sulfite helps "detach" some of the mordanted argentothiosulfates from the image silver, but I haven't seen a lot about this anywhere. Personally, I'd rather not rely on the wash aid to ensure proper fixing of my fiber-base prints... I'll continue to use two-bath fixation and err on the side of undershooting the capacity.

Quote Originally Posted by Rafal Lukawiecki View Post
Doremus, I hope I did not make it sounds like I was ever suggesting that KRST is a fixer. ... I am merely curious, however, if the presence of 3-5% of fresh ammonium thiosulfate in a working strength KRST ... would have a positive effect on the process of desorbing of the complex argentothiosulfates. I hope you will agree this is a valid question to ask, ...
I don't know if the presence of ammonium thiosulfate in KRST helps in desorbing the argentothiosulfates... In fact, I'm not really sure why it is present in the toner to begin with. As you know, I replenish and reuse my KRST. I have gallon jugs that have been going for more than five years (more like 10). I'm sure that the ammonium thiosulfate in these toning solutions is as good as gone, but they still tone just fine (and don't have the annoying ammonia odor either). I'm curious as to what the ammonium thiosulfate is there for in the first place.

And, I'm not a chemist either, although I have a few university-level chemistry classes behind me and I've been reading about and dealing with photo chemistry for some years now. I would always defer to Gerald Koch or PE or any of the other experts on this forum. My responses here are as much about learning as about giving information to others.

My main point in my previous post, however, has less to to with chemistry and more to do with using time and resources wisely. It seems to me that you are spending an awful lot of time and effort trying to compound your own fixer and invent a new fixing process. Kodak (under Haist and others) and Ilford have done the research on fixers much more extensively and better than I could ever hope to do without dedicating a career to photochemistry and experimentation. I am happy to use their research and conclusions. There are a number of well-documented ways to fix and tone properly. Maybe you could spend your time better using one of those? Unless, of course, your goal is to explore photochemistry and fixer compounding. For me, I'll use my limited time to make prints using time-tested methods. I don't have time to spend re-inventing the wheel, so to speak.

And, never any offense taken! You need not apologize to me about a lively exchange of ideas.

Best,

Doremus