Tue, 12 May 1998 16:52:54 -0400 (EDT)
My guess is that you are seeing a version of what sometimes happens to very
old, improperly fixed and/or washed silver prints, that is, migration of
excess silver to the surface. Depending on the concentration of the silver and
the size of the grain clumps it may appear silver, blue, violet, brown etc.
Try exposing a piece of paper to light from the enlarger, put it in
the developer tray for maybe tens seconds, dunking it in stop bath for a second
or two and turn on the white light. My guess is these are prints that were
underexposed so were thrown in the sink before fixing. Maybe they got splashed
with a little stopbath or fixer.