I have a small issue. I have several split boules of synthetic ruby and am having problems finding a gem drawing with a short (p+c+0.02)/w ratio. I also have a lot of aqua that is kind of flat needing the same sort of gem diagram. I’m cutting a ruby for grandma’s 100th birthday and want a nice large stone for a pendant or something like that. It is 10.6 thick at the butt end and 19mm wide 1" up from the butt end , and 10.3 mm thick 1" from butt end. I have Gramms books and am looking at something called Suz’s Bar that’ll be large and long. Has any seen this cut in ruby or red garnet? Any ideas of another good cut for a split boule as described (I’m also looking at ZIP and Long Shore Man). I’m not that good but I suspect my Grandma would wear a gem made of limestone if she knew I cut it. If she likes it, I’ll promise her for a big hydrothermal colombian emerald for her 101st bday.
I’m thinking of cutting Tabula Rosa by Tom Herbst
There is no need to go to such a thin stone as Tabula Rosa, which is used for dark garnet which won’t return light. Tabula Rosa is designed to “window” rather than return light and with corundum you have a high RI and the potential for lots of sparkle, so use a design that does not window. Even if you used all 19mm of width, you would still have a depth of 0.54. I did a trial cut in GemCad and did a square stone with a 43 degree pavilion and a 10-20-30 degree step crown. This works out to exactly 0.54! Since you are going to (you are, aren’t you???) put on a crown, you won’t be able to get a 19mm wide stone. I’m guessing you will have something about 16mm wide. At that width, you have 0.62 depth. You should be able to find a number of designs at about this depth. IDK what the ideal pavilion angles for your design would be, but for corundum, my experience leads me to believe you could get good light return with about 40 degrees. If you are running out of room (depth) as you cut the crown, you can always lower the angles with not too much effect on your light return performance.
You have not said what L/W ratio you want to use, but I would not go too long, because light return in tilt on the long axis suffers a lot when you do, esp. if you are using a keel on the pavilion. If you are thinking rectangle, I would use something like L/W or 1.25 to 1.4. This would give you a 16x20 to 16x22mm stone and you could find a commercial mounting in silver (or gold) for this stone. If you get much larger than that, you are going to be looking at a custom mounting and the costs associated with that. Remember that a 16x20 stone is quite large and in corundum it is going to come out over 20 cts! If you want to go this large, make sure Grandma likes to wear big stuff…some people don’t!
You can look at designs at facetdiagrams.org. Use the search function and search only for open designs. You can print out the cutting instructions for those. If you pick something in particular from there, I can optimize it for you and send you the pdf for the revised design. Good Luck!
Thanks for the information.