How to clean a hanging shell light shade?

It looks like glass oyster shells (Capiz shells?) strung on clear monofilament hanging from wire hoops, with a decorate shell & metal "crown" at the top.

It's pretty. It's been hanging in the attic since before we bought the house - so at least 8 years of dust & "stuff" on it. The shells aren't too bad but the "crowns" are brown with dust.....

How do I clean them without dissolving the layers of calcium making up the shell or damaging them? I have no idea how these are glued or otherwise held to the metal parts of the "crowns".

No wiring involved - this is just a pendant light shade - so water-based cleaners shouldn't cause problems, since I can assume the shells CAME from water creatures!