well, in the case of the gelatin tin types i have been told it both brightens and lightens the image
(because they have less luminosity ( duller? ) ) so my uneducated guess is that MAYBE it will do the same thing
i plan on trying something like this tomorrow ... i have some ancient liquid light, and some way-fogged paper that i can just
develop in room light ... i will try to post my results in this thread too
bon chance !