Not to throw any nails into the concept of toning, but I believe I might have read on APUG that there is some information that states that Selenium toning does not add any meaningful longevity to a print ( work at RIP? ). The most important factor(s) might well be that all traces of fixer are removed, and the any mounting materials are completely archival and free of contaminants of any sort. There are obviously photographers who use a dilute solution of Selenium in order to influence the color of the finished print. Such "toning for color" is not at issue. As is the case with many "facts" about photography, it would be interesting to know of any scientific research that definitely proves that toning prevents degradation-or, has no affect at all on longevity. Selenium toning has become thought of as a "necessary step for longevity", and has been promulgated as "necessary" by experienced photographers who have had such information passed to them by other photographers and books. We have taken such information, perhaps, as being true because of our respect for our teachers and colleagues. However, are they correct? Simply asking for information of a scientific and unbiased nature....not starting any arguments here. Indeed, if it can be shown that Selenium toning is NOT needed for longevity, then another chemical step that can affect the environment, and uses additional water, MIGHT be avoided. Thanks.
Ed