Dear Ross,

Thank you very much for your circumstanciated reply.As far as the practice
of oiling shells is concerned, I can accept it if it preserves the
periostracum that might have a tendency to peel off after some time in
rather dry conditions.I can also understand conchologists who like to use
make up ( oil)to enhance the colors. But is there scientific evidence that
the oil otherwise " preserves" as you state it. If so, I would like to hear
about that evidence from you or anyone who might have it.I suppose any
shell has a quantity of H2O in it. Does oil prevent the water to evaporate?
Should we prevent water to evaporate? Does oil prevent colours to fade away?

I further reviewed some posts and read with lots of interest one dedicated
to lip filing in conus and other shells.

My question at this stage of the discussion is: is there any means of
finding out by  simple observation whether a shell with a natural gloss
(cypraea, oliva, marginella and even some conus) has been enhanced by means
of polishing powders?
Best regards
Charles