Re: Toning and Permanence
Iodide treatment is only weakly effective. It's inadequate to completely protect the image from standard peroxide attacks, while polysulfide toning is sufficient.
Efficacy of selenium treatment is dependent on the emulsion and developer, not only on the toner solution. It is not very easy to determine whether selenium treatment is adequate or not for ALL silver-gelatin material used today. Several studies indicated that selenium is effective with some emulsions but not in others, all at the same concentration and same treatment time. It is also known that selenium treatment may protect dark areas better than light areas, which may be left unprotected. These are the problems with selenium. Polysulfide treatment does not leave this problem.
There is a product called Ag Guard. I have some detailed discussion here:
http://www.silvergrain.org/wiki/index.php/Ag_Guard
This product is well tested by Fuji people, and the result is very promising, especially when polysulfide cannot be used, or when full toning with selenium is undesirable. However, this product is not available outside Japan. I have been making a image protecting agent similar to this and also has very good image protecting action. It's been showing pretty good protection by bleach (immersion) tests and peroxide fuming tests. I should be able to report more details in near future.