Back to IGS | FAQ | Contact

Lowering Angles For A Facet Design

Just asking if i can lower the angles on the pavilion from 41 degrees to 38 degrees if I do all the same. As in every angle is going down -3 degrees from the pavilion to the crown. I have faceted this design many times with Oregon Sun stone and they look amazing , I have purchased a very juicy tourmaline that I am going to facet. It fits this pattern size wise i have measured it and all but not the Problem is most designs I work with are at 41 degrees. Can I Lower Them??

38 degrees is the critical angle for tourmaline, so it’s better to cut that a few degrees above the critical angle. Really, 41 degrees is a pretty good pavilion angle for tourmaline. I sometimes cut the pavilions at 39 degrees, but really prefer 40 to 42 degrees for the best optical performance. If you go too shallow, you’ll get some windowing or tilt windowing. Even though it’s not supposed to work quite right with some designs, I often subtract or add to all angles in a diagram equally and don’t really have any big problems because of it.

I agree with the post above. I would cut it at 41 degrees. If you cut at 39 and your machine is off the smallest amount you risk windowing. Also there is the human factor of possibly setting the machine off by a quarter or eight of a degree. Happy cutting

Wow i had it wrong then , lol i thought you need to cut the stone at the critical angle. Thanks so much for the info and good responses, will go forward to cut the stone into the design i wanted to and do so at angle 41 :slight_smile:

You should check on the reflective index for that stone to get the best angle.
The SRB cut is 42 degrees for the pavilion mains but the next time you work on a sunstone, try cutting the mains at 45 degrees and the first facet crown at 40 degrees. Adjust angles on the rest of the cut accordingly. I think you will be amazed at the brilliance of this stone when you are finished.

This tip was given to me by the owner of the Double Eagle mine and the steeper angles match the RI of the Oregon Sunstone perfectly. I was amazed at the difference from the brilliant stones I was previously cutting, this cut came out more brilliant.

As for your tourmaline, its RI is around 1.6, quartz being 1.55. So I think, in my humble opinion, that you don’t want to lower the degree setting to 38, you may wind up with some black edges on the finished stone.