Quote Originally Posted by Doremus Scudder View Post
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.
I've been looking for information on that for a while and came up empty. Fact is that the Selenium in selenium toner is so toxic that few home brewers are willing to mix this toner from raw chemicals - at least I definitely wouldn't. Therefore I don't think we will see much published data on that.
Quote Originally Posted by Doremus Scudder View Post
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.
Among the later books on photo chemistry are Haist's two volumes, and these books don't even mention Ammonium Thiosulfate. Why? Because Kodak would have stomped on Haist's feet if he would published trade secrets! What does this tell me? There isn't much published about modern fixers, at least not with solid data and reproducible results, and even patents are mostly vague or intentionally misleading. Most published data (formulas and test results, not instruction manuals) on fixers is simply not applicable to modern products.

Testing, at least at amateur level, is much easier for fixers than for developers. Measuring speed and grain (as Mark Overton did) requires some apparatus, and measuring sharpness (reliably!) is beyond reach for most of us. Measuring clearing speed is trivial, and tests for residual silver and hypo are cheap and available, with published recipes. The biggest obstacles to fixer improvements at the amateur level are the cheap availability of commercial rapid fixer (most of the time these commercial soups cost half or less of what the raw chems would cost us!) and the fact that fixers don't visibly improve your prints (for the first 10 years at least).

Is there a motivation for home brewing or testing fixers? Apparently TF-5 fixer runs circles around standard commercial rapid fixers, especially in terms of working solution life, but it's economically unfeasible to ship it across continents and its recipe is unpublished. A version of Farmer's reducer would be nice that has a working solution life of 8 hours (one really long dark room session). Likewise there is little to no data available for alkaline fixers, or even just simple data points like "what's the most economical way of archival fixing for TMX/TMY that leaves no magenta stain?" or "how can I translate a fixer's clearing time of film X into archival fixing time of paper Y?".