[skahde]

Stefan, as someone who has worked with chemicals almost all my working life I don't take everything in MSDS/COHSS data as gospel.

At some point writing MSDS was part of my job and I therefore know there limitations very well.

Photographers found from experience that Pyrogallol was more toxic than Hydroquinone not through a few experiments with lab rats.

But what kind of experience? Described where? Observed and confirmed by who? As long as there is no kind of evidence given I'd rather trust the rats.

What you are calling rash statements are just accumulated knowledge built up over a number of years.

Have a look at eg. Richard Henry "Controls in Black and White Photographie" and see how much of that "accumulated knowledge" turns out to be well ripened myth when really put to the test.

We don't need to read the original papers and sources because history has informed us how to safely use these chemicals in our photographic practice.

Ian

No, I don't think knowledge does accumulate. In my view it is lost over time once it has been established. What you describe is a situation where nobody refers to the original papers anymore but information taken from them goes from ear to mouth into publications, out again taking another round, loosing shape and contents to a degree where the original statment is hard to be recognised or lost alltogether.
As a result, there is lots of "wisdom" around which has little to do with what was meant but lots of procedures are in use which obviously work but there is little in-depth knowledge around why and in some cases why not. That is where we are: Photography is as much science as it is craft.

But coming from the craft-side one shouldn't pretend to do any kind of science or make statments beyond that somethings "works" within the craft. There are clear rules how to part assumption and myth from knowledge (as limited as it might be) build up over times much longer than photography exists. Not sticking to them is a weekness often accepted by authors for a reason: Emperors new cloth.

best

Stefan