Dear friends (so: to everybody! And expecially to Guido Poppe! ;-),
I have spoken with some tecnicians in my labs: to resist to a solvent like
acetone, the false cowries should have been painted with
1) an epossidic resin, or
2) an "epoxy-poly-ester" (sorry for the translation!) resin
and then "cooked" into an owen.
They are also called "paints for electrostatic applications".
We can discover them in 3 ways:
a) under an UV light (Wood lamp: also portable and cheap exists) they
(expecially the first) become yellowish
b) I can confirm that methyl ethyil ketone is a good suggestion
c) once fixed, they are extremely fragile: some soft stroke with a wooden
hammer should create thin fissures (like cobwebs) in the paint (obviously,
not in the external part of the cowry: hit gently!)
Hope this could help
Sandro (from Italy)