Sodium Sulfite as hypo clear?

Rudeofus said:

AFAIK selenium toner is a mix of some selenium salt and lots and lots of Ammonium Thiosulfate. Ammonium Thiosulfate has a pH of about 8 and will therefore smell like Ammonia. Over time it will lose some Ammonia and the pH will drop to a point where it does no longer smell. Absence of Ammonia smell is therefore no proof for absence of ammonium ion.

You can trivially test, whether your selenium toner contains Ammonium Thiosulfate: take a very small sample and add Sodium Hydroxide: if it smells like Ammonia, then there was ammonium ion in solution. Then add a strong acid. If Sulfur precipitates, then you likely had thiosulfate ion in solution.

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Sorry to chime in, but is pH of selenium toner of importance? I.e. whether it helps to speed up the toning.

iakustov said:

Sorry to chime in, but is pH of selenium toner of importance? I.e. whether it helps to speed up the toning.

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Yes, it is. Ammonia is used to keep the pH high. As I understand, if the pH drops, the selenium tends to drop out of solution rendering the toner unusable.

Rudeofus said:

AFAIK selenium toner is a mix of some selenium salt and lots and lots of Ammonium Thiosulfate. Ammonium Thiosulfate has a pH of about 8 and will therefore smell like Ammonia. Over time it will lose some Ammonia and the pH will drop to a point where it does no longer smell. Absence of Ammonia smell is therefore no proof for absence of ammonium ion.

You can trivially test, whether your selenium toner contains Ammonium Thiosulfate: take a very small sample and add Sodium Hydroxide: if it smells like Ammonia, then there was ammonium ion in solution. Then add a strong acid. If Sulfur precipitates, then you likely had thiosulfate ion in solution.

Click to expand...

koraks said:

Yes, it is. Ammonia is used to keep the pH high. As I understand, if the pH drops, the selenium tends to drop out of solution rendering the toner unusable.

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Rudi,

I'm not sure what's going on with my replenished toner; just that it works. If the pH is low enough that the ammonia smell is gone, but the toner is still active, I'm happy
Next time I have some reagents handy, I'll do your tests. I don't have sod. hydroxide on hand normally, nor acids except for acetic.

Koraks,

Maybe some of the precipitate I see is selenium dropping out of solution. On the other hand, since the toner activity is fairly consistent and long-lived, it must not be much, since having a lot of selenium precipitate out would reduce longevity. Part or all of the precipitate may be silver or a silver compound. It would be interesting to find out what's really going on.

I've never had a toning solution "die" on me; it loses activity slowly, which then comes right back up with the addition of a small amount of toner concentrate. Like I mentioned earlier, I might add 15-20ml of concentrate per liter after toning times get too long. Right now I'm toning about once a week, and tone about 20-35 prints each session. I'll replenish every three or four weeks, so that's somewhere in the neighborhood of 80-100+ 8x10s per liter toned before I replenish. That's pretty good life expectancy fr the toner, I think.

Best,

Doremus

I have the same experience... the stuff gets slower/weaker, I add some more concentrate. I have a coffee filter that rests in a funnel to strain the black stuff out, though I've never seen that stuff damage a print, it just rinses away. If I'm doing something where the toning is critical or making an "edition", I'll mix a batch specifically for those prints so I can time it and repeat it though.

Toning by time only works for a few prints, since the toner loses activity the more prints are run through it.

I tone visually, then note the time if I have more of the same print to tone. I'll tone those at the same time, keeping an eye on them, but that's usually only two to four identical prints. However, after you run 10-15 prints through a usual size toning bath (e.g., 1 liter for 8x10 prints etc.), then the time to tone to the same level will have increased noticeably. Those that tone everything for x minutes in toner 1+x aren't getting even toning...

Plus, I've found that to get the same "look" for prints with markedly different distributions of tones, that toning times for those prints may be quite a bit different. It's a subjective evaluation of overall toning, which is affected by the relative amounts of highs to lows to mid-tones.

Doremus