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)