How to clean specimen seashells
After the collection, the best way to kill the animal is freezing it alive. It is also what preserves most the shell and avoids the acid rejections after the death of the animal. Defrosting should be slow to avoid thermal shock and cracking on the polished parts.
Once the animal has been removed and the operculum put aside if necessary, the shell should be soaked in the most concentrated, pure and additive-free bleach. When bubbles cease to form, the shell should be removed from the bleach immediately and rinsed under warm water, then soaked for at least 24 hours in clean water at room temperature.
Calcareous deposits will be removed mechanically using a stainless steel punch (large thicknesses can be trimmed with a quick drill and a sculptor's tip). A cutter blade can also be used to remove the last traces of periostracum.
Finally, apply a generous layer of pure and acid-free mineral oil (never vegetal) on the shell with a painter brush, let soak for an hour, then wring the surplus with a smooth paper towel.
Here is a series of photos before / after that show the results obtained using this technique: