I’m polishing a synthetic spinel and the table is starting to show pits. At first everything seemed to go well with my BA5T lap with 100k diamond and then the facet edges started to show chips. I moved to the Darkside and stayed using aluminum oxide and got the chipped edges removed. Then I started to see small pits which I slowly tried to work out. Then I got a groove (not scratch) which I am now trying to work out.
What else can I do? I’m working on a competition stone and would like sharp meetpoints. Should I use another lap? What else can I try/do?
What you may be seeing is the dreaded orange peel which spinel happens to be prone for that. For one thing I never use a 1200 lap on this stuff but rather go directly from my 600 sintered to something higher like 3000. For some reason that seems to avoid the problem. If you do encounter orange peel you have to back up in grit size. For example encountering it at 1200 you have to go to 600 and recut or waste a lot of time. Pits resulting from bubbles is unlikely in sync spinel. Keep at it. Spinel cuts beautiful stones a good seller for me.
50,000 to 60,000 grit is the finest diamond i use for polish. i have a 6″ batt TIN lap and i run the speed VERY slow with a VERY slow water drip. a make a muddy slur of the powdered diamond on lap with appling powder on lap with finger. we do most all stones that way and polish quickly. had no problem on spinel. and with slow speed and water we dont throw of the diamond and dry out the lap. on very large stones we sometimes use a drop or so of a light oil or crystal lube. on really large stones we’ve made hard wood laps(maple or oak) and use crystal lube and diamond on that–NO WATER–