If I may weigh in again, this time regarding testing, experimentation is the ultimate test. My graduate school mentor, a theoretical chemist, used to say "theory proposes, experiment disposes."
From that point of view, much of the discussion in this thread is speculation with a relatively small (albeit non-zero) component of science.
With regard to experimentation, the ultimate test is not how pure the chemical is but whether the grade of the chemical in question is "fit for purpose." Therefore, the true test is functional testing, not purity testing.
Purity testing may play a role in the bigger picture. Purity testing, together with other appropriate experimentation, may help the researcher identify which impurities may adversely affect function. The testing itself will not tell us whether an impurity may adversely affect function, but it can be one component of the larger research plan.
In addition, purity testing can be one component of a Quality Assurance/Quality Control program, i.e. a way to make sure that product quality is and continues to be adequate for the task.
However, let me reiterate, it is only functional testing that can truly answer whether a certain grade of chemical is fit for purpose. Purity testing is only an adjunct activity. It is not even a necessary activity, provided that one could assume that the quality of a raw material does not change in quality over time. (A sometimes dangerous assumption, but I will reserve that discussion for another time.)
Therefore, it is only functional testing that will tell us whether food grade chemicals are adequate for photographic applications. All pronouncements in the absence of such testing are speculation. Perhaps informed speculation in some cases, but nevertheless unproven statements.
There may be good reasons for someone to decide not to perform the tests needed to prove whether food grade chemicals are adequate for photographic applications, but those good reasons to forgo testing do not constitute a substitute for actual testing.
I'm not sure I am making that last point clearly enough, so let me put things another way. I would not blame anyone for refusing to perform the testing required to answer the question. Furthermore, I would not bar anyone from expressing an opinion on the probable outcome of such a test. (An opinion on the probable outcome would be characterized as a hypothesis.) However, in the absence of the actual testing, the opinion, even an opinion from an expert, remains unsubstantiated... perhaps fodder for interesting conversation and debate, and maybe even useful for rough guidance in the absence of established results, but unsubstantiated nevertheless.
I'll give Patrick this much. He is willing to experiment. I have not followed all his work, and I will not judge the overall quality of his work in this post, but at least he is one who seems to be willing to do experiments. This is not to say that he always takes on the challenge of proof by experimentation, but on the whole he seems to be of an experimentalists frame of mind. On the other hand, it seems to me that Patrick sometimes has a tendency to reject criticism if his work too quickly.
I'll say this about PE. He is a highly experienced and knowledgeable expert whose opinion needs to be carefully listened to. However, at times PE also seems unwilling to do the experiments needed to back some of his claims made in posts, and may at times be overly sure of his opinions. As I said, there are often good reasons for declining to do experiments. It can sometimes be difficult, expensive, lengthy, and unrewarding work. However, expert opinion in the absence of experimental verification remain interesting (possibly even useful) speculation, but speculation nevertheless.
One other thing is clear. Neither Patrick nor PE seem to be able to read, integrate, and carefully consider all of what the other person is saying. That is a fancy way of saying that they don't listen to each other very well. This much is clear from even a cursory reading of the running battles they have been having with each other. This seems obvious to me as a an observer with no ax to grind.
There are too many instances where factual matters seem to have been ignored by opponents later posts. When I say "factual matters" I am not referring just to scientific issues, but mainly to historical fact, i.e. who said what, when did they say it, etc.
I actually enjoy part of what comes out in the exchanges between Patrick and PE. However, at times it also becomes almost too painful to watch, especially when it deteriorates into tit for tat exchanges.
, which do you want? Emulsion work and a textbook with all of the experiments and data, or my chasing a will of the wisp that I have seen, caught and identified over 30 years ago?
