the following information comes from IPI (Image Permanence Institute) and from Tim Rudman's book "Toning Book" . Check Archival permanence in that book if you wish.
The following is a quote from IPI "Selenium and gold toning only provided protection in proportion to the conversion that take (s) place, and even at high levels of toning protection was incomplete.
Kodak Rapid Selenium Toner gave very little protection to the highlights and mid tones when used in high dilutions, as is often recommended for archival toning."
(my comment: remember selenium works from the shadows up; gold from the highlights down)
Tim Rudmen"s quote "Advice that selenium toning at high dilutions of 1:20 or more will give good image protection without colour shift should no longer be followed. Toning for permancence should be at 1:9 or stronger for at least three minutes at 68 and colour change on these papers is usually inevitable, if reasonably full protection is to be achieved. "
Tim goes on to indicate that a Sistan treatment may help with additional protection, but "I AM NOT AWARE OF ANY HARD DATA ON THE EFFECTIVENESS OF THIS COMBINATION".
Some where in the files i have some information about the IPI findings, but can't put my finger on this right now , but a little voice is reminding that at high dilutions ratios the time was something like 8 minutes for completion and with most papers you will get a color shift.
Last year we ran a lot of test ( and continue to do so, *got behind*
) on various papers with various toners. The most resistent to color shift was Luminous Fiber cold tone paper. In a selenium ratio of 1"15 after 10 minutes there was a slight shift in Dmax but no color shift. Now this is just our experience with our equipment, etc. this was not a scientific study under controlled conditions.
This is one reason i have been playing with Les"s extending toning treatments (that is not his term, but mine). One hour in 1:10 Seleium, Oriental Seagull graded paper at which time there is occurs a color shift some where between 8 to 10 minutes, and can still be seen after 1 hour altho less so, and then after 90 minutes in gold the color has completely disappeared with increase in dmax and a different sense of dimenison.
Oh yes one other statement that comes from IPI. With regard to the effectiveness in terms of archival protection. This is the list in descending order:
Polysulphides
selenium'
gold
platinum
"this assumes full toning".
hope this is helpful.