Cutting angles of gems

[lonewoodminer]

Hi all

I would love some ideas on the best cutting angles for darker compared to lighter stone to bring out the best in a gem.

Cheers Andrew Lane

 

[Garry H (Cut Nut)]

Buy GemCalc for $320
email me on garry at ideal-scope.com

 

[Richard M.]

Date: 4/1/2005 3

0:56 AM
Author: Garry H (Cut Nut)
Buy GemCalc for $320

Would you please provide more information? Will GemCalc help me turn my too-dark spinels, garnets, sapphires, etc. into brilliant masterpieces? Or will it merely give the usual advice of cutting pavilion mains at or below the critical angle to slightly window the stones and let more light through? If so I can save $320.

Richard M.

 

[Michael_E]

Andrew,
My experience with cutting darker stones, like sapphire and garnet is that you need to cut them as shallow as possible in order to have the light path through the stone as short as possible. There are two problems with this however. The biggest problem is that if you make the stone too shallow, the brightness falls off dramatically and you defeat your purpose. It''s kind of a balancing act between crown and pavilion angles to get short lightpaths and good brightness. The next problem, at least in sapphire, is that often the "A-B" axis is green while the "C" axis is a very nice blue. Assuming that you can orient on the "C" axis to get that nice blue, you then need to be concerned about having as little green as possible show through. The problem lies in that if you cut the stone shallow, you will have a larger green component, as the light path on the green axis is maximized. What you end up with is a nice blue stone that becomes more green as you approach the girdle, sort of a bullseye effect. Since your financial return is based on both color and size, my advice would be to cut the stones to a size that gives you the best color, as this will be more saleable and you can turn your merchandise faster. Even if you have to cut those large 20 carat stones down and turn out a bunch of good blues at 1+ carat you will still make decent money from them and not be waiting around for that one person who wants a large dark stone.
After looking over the specs of GemCalc, I would have to say that this, in combination with GemCad may be a perfect software combination to model different cuts and come up with combinations that give the best color for you. From the description on the Octonus site it sounds like GemCalc will deal with stones that are dichroic and can show you best cut angles for best color and brightness in the finished gem. Then all you need to do is size your material appropriately. Does your cutter have GemCad already ?

 

[bar01]

How about getting a hold of Richard Homer? Some great before and after photos - Like These

 

[Matata]

Faceters.com has some great info.

 

[lonewoodminer]

Hi all

Thanks for all your comments, I feel a bit embarased about asking as I should be an expert on this too, but Im afraid Im just not and trying to learn .
No our main two cutters dont have any programs such as Gemcal and are pretty set in there ways, I have disscussed with them trying some differnt angles but they always seem reluctant I hope If Im armed with some more evedince I can convince them to try something new to them. Some of those before and after shots of Richard Homer are great, what a change!

Cheers Andrew