recently members of my club and students have been coming up with small montana sapphires they have collected on road trips there. and ya we see a lot of them have what looks like pitting. we use either a 1200 or 3000 metal bond((plated) diamond disc that some call toppers which we all prefer here and much cheaper from china. when we see a pitter facet we cut it not all the way in to the mark and instead polish it in, just take a little longer. we use a tin lap very slow speed with diamond powder and very slow drip of water to make a muddy slur– no oils or pastes. and we have very good success. as to the sintered lap some are so proud of i wouldn’t own one. they are high priced and a waist of money. they are diamond grit mixed with metal powder then fused together to a lap. the diamond is not all on the surface so your not getting any use out of it and as your stone starts wearing away the metal, like in a saw blade, the surface changes. no thanks from 1968-1977 i worked for crystalite making/plating those metal bonded lap and you have a mass of diamond surface. the china ones have even more diamond than those made here. a for sintered ya they last 20 yrs maybe but a poor cutting surface. i have my crystalite’s from then, from 1968 an still use them just fine and the coarse ones can be sharpened up just like a saw blade. gemmakermz@cs.com