I don't collect those type molds but I assume they are smooth.

I'd start off with a tooth bursh and that pink stuff (star brite or something like that) - no water.

Then I'd use 320, 400 & 600 grit sandpaper with a drop of oil. I might finish up with 0000 steel wool.

By this time all dirt, hair-line scratches and hopefully that greenish film will be gone. Presto - new chip.