3 new cameos

I got 3 new ones today! 1st is a beautiful shell carved, trombone clasp with tool marks. Although, she doesn't have tons of marks like the far left. That one you can see every little mark that was made (on shell). The middle one, is having a hard time. The brass had some metal exposed and it's rusting lightly, as well as the chip she has on the lower left hand side. But we believe she's celluloid or whatever. She's a clinker (how I describe the noise of shell on teeth) and cool to the touch. It looks although, like she's glued onto the back, but you can't get anything under, but can't get thestuck on dirt.

Any advice on how I could possibly stop the rust from occuring? I don't want to damage her either way. I don't like damaging any of my cameos real and fake.

A lady I've been talking to, who's collected cameos for 40 years, does all sorts of nifty little things with all her cameos. Trying to think of ideas for the fake ones to be crafted into something, and have some ideas on how to display the real ones.