If the stain just adds base fog, what gives the negatives their wonderful qualities?
I will test it and see how I like it. Thanks.
Stain is only one of the attributes of pyro staining developers. Such developers also tan and harden the gelatin of the emulsion, which can lead to a more precise reduction that increases sharpness.
Sandy King
Note that hydroquinone, a very common compound of developer solutions, has a toxicity in the same range as pyro. When in dust form, these two compounds can have real bad health effects if absorbed.
Have you any good data for this? My own very limited knowledge is that even in the places where they actually sythesise(d) hydroquinone, there is no persuasive, let alone conclusive, evidence that the stuff is significantly dangerous. Of course you may have better information than I.
As for the toxicity of pyro, I rather like the words of Mike Gristwood, late of Ilford: "There are some things you worry about your children doing, and some things you worry about doing yourself." He placed the use of mixed pyro developer in the former category, not the latter, though like any sane person, he would use all reasonable precautions in mixing it. Of course he was speaking on his own (very well informed) behalf, not as ex-Ilford.
Have you any good data for this? My own very limited knowledge is that even in the places where they actually sythesise(d) hydroquinone, there is no persuasive, let alone conclusive, evidence that the stuff is significantly dangerous. Of course you may have better information than I.
I'll go along with that. But the toxicity data for hydroquinone specifically refer to the ingestion of large amounts, or industrial-scale exposure to dust. This is not, on my reading, the same as the toxicity of pyro.I wouldn't swallow the thing.
Dear Sandy,What part of MHV's message are you questioning? Pyrogallol and Pyrocatechin are in the same class of reducers as Hydroquinone, and MSD data sheets clearly indicate that the three substances are very similar in terms of toxicity issues.
Virtually all reducers have some toxicity issues but if treated with reasonable care one should not IMO be concerned about normal use. By reasonable care I mean, don't breath the powdered chemical, and avoid to the extent possible prolonged contact with the skin. That should be covered by mixing the chemicals in a well-ventilated area, outside if in doubt, and wear gloves if you develop in tray. For most types of development (in tanks, tubes, etc.) it is easy enough enough to avoid any contact with the developer so gloves are probably not even necessary unless you keep your hands in the developer for long periods of time, as in shuffling in a tray for example.
Sandy King
Dear Sandy,
Your point is the same that Mike was making, and that I attempted unsuccessfully to convey: no problem in normal use. My own reading -- which may be biased from preconceptions, plus the almost complete absence of reports of problems in hydroquinone fabrication (Kodak) -- is that pyro is a good deal more dangerous as inhaled dust than hydroquinone.
Cheers,
Roger
Hi Roger,
You may be right about the inhaled dust issue, but in the absence of compelling evidence to the contrary, and given the close chemical similarity of hydroquinone to both pyrogallol and pyrocatechin I am still inclined to believe that inhaling one is about as dangerous as the other. I strongly advise against inhaling any of these chemicals and recommend that one take positive measures to not do so.
We appear to be in agreement that in normal use there should be no problem in careful use of developers containing any of the three substances, or of most other reducers which may have toxic issues.
Best,
Sandy
If the stain just adds base fog, what gives the negatives their wonderful qualities?
I will test it and see how I like it. Thanks.
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