It has been a bit, but I finished a tourmaline gemstone today that is worth commenting about. The rough was a pretty average piece of dichroic brownish gold that had be reduced significantly to eliminate a major flaw. And I decided to cut an oval with a ratio of 1.5 which is as extreme as I usually cut.
The rough was probably from Zambia and I have cut quite of bit of material that is similar. It both cuts well and polishes well. The pavilion worked up well and the I experienced only a little undercutting until I reach one of the ends. I was with one facet from finishing the pavilion when a C axis polishing problem ripped the facet. With my use of alumina/vinegar and a stationary lead/tin lap I find that the c axis can be completely different than polishing the a/b. In this case I think that I let the waste build up too much on the lap and with a more fragile and reactive c axis, the facet failed. I ended up having to regrind the facet with my well worn almost dead 3000 grit lap and repolish about a quarter of the pavilion. It all went well and the transfers went well so I was in a very good position to finish the crown. Now I really don’t use meet point except to get a good shape for my girdle. But I do use the suggested angles for a meet point design, or at least I try to. With this stone, something happened that has never happen before on any of my ovals.
I CUT THE OVAL’S CROWN WITHOUT MAKING A SIGNIFICANT CHANGE IN THE MEET POINT ANGLES IN THE PATTERN AND THE CROWN CAME OUT WELL.
I never expected to see it since I adjust many cuts by eye as a work up an oval. But there it was an oval by the numbers. (I don’t use the meet point cutting sequence) I never expect to see it again. I hope to get Jeff to take a picture and I will attach it to this post. (I have another tray to have photographed), but it is not an exceptional stone unless you can tell that I did it by the numbers.
Bruce
