hello, i have been trying to cut a very pretty piece of green oregon sunstone. in general, i have found sunstones to be very easy to cut and particularly polish (and they look so good at the end that i love cutting them). however, my recent piece (the green one) has a very tricky facet. i noticed in the pavillion cutting that one of the facets was cutting much much faster than the others – i thought this was interesting and made note to be careful not to overcut. everything looked great as i approached the polishing stage.
however, all the facets on the pavillion polished very quickly and beautifully as usual except for the same facet that had cut so quickly. the tricky facet would get to an almost polished stage and then the scratches began. not matter what i did i could not stop it from scratching. i tried cerium oxide, tin oxide, and chromium oxide. i have not yet tried diamond – but probably will next.
i suspect that i somehow managed to line this trouble facet up with a cleavage plane but that is just a guess.
i am wondering if anyone has any tips in this regard. i am also considering changing the angle slightly to see if going “off plane” from the “presumed cleavage plane” will help.
Cleavage plan is usually not a issue when cutting Oregon Sunstone. It depends on the crystal growth it self. As in other rough crystal you may find a hard surface, which makes you think your lap is not cutting, as well as a soft spot sometimes.
I have worked with a lot of Oregon Sunstone rough over the years and the soft spot is caused by soft end grain of the growth plates in the crystal. It is like trying to polish the end of a board, end grain. Try a soft touch and be patient as it will take longer as you may be going against the grain and it is trying to feather. If that does not work try reversing your lap so you go with the grain, remember a soft touch here also so you don’t jam your stone, done that not fun.
I have had good luck with Jon Rolf’s Greenway. That is all I have used on Oregon Sunstone for a couple of years now. It will move your meet points and leave a polish at the same time. I cut with a 600 to a broke in 1,500, then straight to the Greenway for meet point and polish. Make sure to break in the lap.
Hope this helps
As John said, try reversing your lap. On those particularly difficult facets, pick the direction with the least amount of damage and persist with the gentle polishing. On most, I’ve found that going to a tin oxide Ultralap (oh, horrors!) was most effective. Persisting has resulted in polish, eventually. Gentle is the key to prevent rounding of facet edges.