I am not sure what is going on with your malachite Vintage Alhambra 10 (or 20) motif. Do you live near a VCA
boutique? I would bring it in and have them look at it. Did it get wet at some point? My 10 and 20 motifs do not seem to ever get dirty and when I am not wearing them they are in our safe. If I were you I find out what is causing this and then have Van Cleef try to restore the stone and polish the piece. Good Luck!