Quote Originally Posted by Photo Engineer View Post
Patrick;

Sometimes it is not what the impurity is, or how much is present, but rather the amount of variability that is introduced by the variability in manufacturing a 'cheap' household product compared to a photo grade chemical.

As an example, Detol contains bromide. Today, most papers are high in chloride and some are pure chloride (or nearly so). Any variability in bromide purity or any iodide salt in any of the chemicals causes a big swing in speed and contrast of chloride papers. Iodide in some salts in developers for films changes the edge effects because iodide is a 'buffer' for edge effects.

So, some hidden or difficult to measure effects may vary and qualitative or eyeball tests will not show it. And, BTW, this becomes even more critical in color.

PE
There is no disagreement there, as far as I am concerned. The disagreement on my part is that some household products may actually be required to be more pure than would be required for photographic use. The analytical reagent use of borax appears to require no more than 99.11% purity. Is that sufficient for medical use? Would we not want to know the nature of the impurities? But because we do not seem to know what the purity of 20 Mule Team Borax is, or what its impurities might be, we resort to something that is certified by some vendor as "Photographic quality" which, for all we know, may have come out of a barrel of 20 Mule Team Borax, and even if we knew it to be analytical reagent grade, we still don't know if it could have come out of the same barrel, simply because we do not know the purity of 20 Mule Team Borax that we get at the supermarket. Talk about assumptions!

Is there some test we photographers could do in order to find out if indeed there is sufficient reason to avoid using the "cheap" stuff? BTW, I don't think cheapness has much to do with my choice. It is more a case of ready availability. If I run out of borax, I cannot run out and get the analytical grade, or the so-called photographic grade, but I can get what I have used for at least 60 of my 80 years within 10 miles of my rural home.