Interesting, I shall have to dust off my pH meter. Then again, I wonder how accurate the inexpensive ones actually are
The fact that sulfite quality may be variable is known since the beginning of the 20th century. The first mention known to me comes from a book of Baron von Huebl “Development of plates with uncertain exposure” of 1919.
And yes, I saw the problem as soon as I made D76 from scratch and compared it to the commercial one. To give you an example, when I make D76 from scratch, using sulfite from any of the two commercial sources available where I live, I do not need to use borax, because the pH would already be 8.5 and the development time taken from a published table will be correct. With D23 I actually had to add sodium metabisulfite to reach the rated pH of 8-8.2, because otherwise I did not get the expected softness and smaller grain. Actually, now for one shot use I prepare Windisch formula, which is roughly D23 diluted with 2 parts of water, pH 7.9-8.0 and develop for 10 minutes at 80 F. If I do not observe the pH, I am certain to get a systematic overdevelopment, which is not fatal, of course, but depending on the film and the subject matter, the results may be less than ideal, mostly “discrimination of highlights” will be affected.
Finally, IMO all strictly metol-sulfite developers (that is without additional alkali) are strongly sulfite quality-dependent, because metol has a relatively steep pH dependence of speed between 8 and 9. With commercial D76 one will get a paradox that with only 20% more metol the development time drops, while common logic suggests that with more developing agent you should get a faster developer. I observed this problem with all developers that contain metol as the main agent in high sulfite, for example Edwal 12, which if not adjusted to pH 7.5 as its author recommends, is a completely different developer. Quite often I was puzzled having found a metol developer without pH listed, because it would be a different beast depending on what pH were set. One such example is the Paul Farber developer, which I voluntarily adjusted to pH 8.8 (to inhibit pyrogallol as a developing agent), but I have no way of knowing if this was the original intention. I hope this rather lengthy explanation helps.
Thanks for the explanation I was a little confused as to what the pH for D23 is meant to be The recipe for it seems only to consist of metol and sulfite There never seems to be any mention of adding anything or having to check pH due to different sources of metol and sulfite leading to the need to re-test for development time and EI
Is it not possible to buy accredited photographic grade ingredients to avoid such problems as you mention? It sounded from what you were saying last night and seem to be saying today in the above explanation that the only safe way to buy a reliable developer is to buy a commercial one as the alternative of home mixing risks the chemicals not being the same each time so what you get as, say, a D23 developer may differ each time it is made ?
pentaxuser
I think what he means is closer to "each manufacturer is different" rather than "each mixing is different." Sodium sulfite from the same manufacturer and the same batch, or the same bag, should have considerable consistency. However, chemicals from different manufacturers—for example, one sodium sulfite labeled as 96% versus one that labeled as ACS reagent, ≥98.0%—may differ in terms of impurities.
You may very well be right but Pixophrenic's reply may have suggested otherwise. It is almost certainly true that enough contamination will cause problems but I wasn't sure if Pixophrenic was talking about matters in the abstract or had suffered the problems he mentions himself hence my questions
Whenever I see something being said that looks worth further exploration I try to follow it up seeking more information
After mixing a batch of fresh developer stock, I do sacrifice some film to confirm proper developer action, just in case.
Can you do this with a "clip test" like the one we use to test the fixer? ... Clip a piece of the film leader and put it in the developer and verify that it turns black?
Your comment relies on an implicit assumption that the chemical industry has not changed in a century. That's not a very realistic viewpoint.The fact that sulfite quality may be variable is known since the beginning of the 20th century.
Your comment relies on an implicit assumption that the chemical industry has not changed in a century. That's not a very realistic viewpoint.
Your comment relies on an implicit assumption that the chemical industry has not changed in a century. That's not a very realistic viewpoint.
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