Guidelines/formulas for telling if your colored stone is shallow or deep?

[beaujolais]

Are there any guidelines/formulas for telling if your colored stone is shallow or deep??

Thanks.

 

[oldmancoyote]

Erm - no. Certainly not general ones. There may be some guidelines for the most "common" stones, but I doubt they would have that much value considering the much greater variety of cuts, including concave faceting, that are available for colored stones.

 

[Proteus]

Date: 8/27/2008 10:17:24 PM
Author:sonomacounty
Are there any guidelines/formulas for telling if your colored stone is shallow or deep??

Yes, but it will be different depending on the gem species. What truly matters is the actual angles that the facets are cut at, because even a correctly proportioned gem can still have very shallow culet facets which cause a window. Since the angles are very hard to measure (and very few sellers give angles,) depth percentages can be used as an estimate to how good the proportions are.

Also, the crown height and pavilion depth ratios can have a large impact on the appearance. For instance, if the crown is very shallow and the pavilion very deep, the average depth percentage may seem to be normal when it is, in fact, quite offset.

Lastly, the cut will also effect this. The proportions for a round compared to say, a cushion or Asscher, will be different.

If you give the cut, gem variety, and depth info (or a picture) I can give you my best guess as to how good the proportions are.

I am very familiar with proportions for colored gems, so I could try to come up with a list of "good proportions" for various gems, but it would probably take a while, and would have to be very comprehensive... perhaps it could start with specific gemstone/cut combinations and go from there, if people are interested.

 

[beaujolais]

Oh, thanks so much Proteus.

These are not expensive stones (at all) but I''m looking at these:

http://www.simplysapphires.com/html/imagesblue2006/bluecns1495j-sm.html

and

http://www.simplysapphires.com/html/imagesblue2006/bluecns1495d-sm.html

I know they are not a big deal but I just don''t want them to be Horrible picks. The larger one has one of the shallower depth.

Much appreciated,
Sonoma

 

[Proteus]

No problem! In my opinion, even an inexpensive stone ought to be cut well.

They don''t give a girdle profile shot, so I can''t quite tell the exact crown/pavilion ratios, but I will give my best guess based on the face-up appearance.

The first stone looks like it has pretty good proportions. It has about 71% depth, and guessing from the photos, it looks like the crown is a tiny bit shallow, but not bad. The pavilion has modified step cutting, which appears to be brilliant-inspired, so it doesn''t window as bad as a lot of those step cuts do. The symmetry is decent on this one, but not quite as good as the second stone.

Your second pick is also pretty good. It''s 68% overall depth. It looks to me that the crown is a bit thicker and the pavilion is a bit shallower on this one, so from the pictures it windows slightly on tilt, but is still quite good for a native weight-retention cut. The symmetry is pretty good on this one.

So in all, my opinion is that you made good picks.

To calculate the depth percentage, divide the total depth by the smaller width measurement. In my experience sapphire/ruby are best around 63%-66% depth in rounds. For cushions, about 65-68% is usually the best. Anything a few percent above or below will still be good, too. The thickness of the girdle can also offset the depth. Native cuts often have chunky girdles, so that''s going to make them appear a few percent thicker than a precision cut stone typically would. And of course, there is always the issue that the facet angles can still make a window. If you don''t see any windowing and it''s within those ranges, it should be a pretty good stone.

These guidelines will also work for stones of similar refractive index, such as chrysoberyl and rhodolite.

 

[beaujolais]

Proteus:

Thanks so incredibly much ! ! What fantastic information. Now I feel much better about these.

Thank you, thank you, thank you, thank you, thank you, thank you, THANK YOU ! ! !

Can I ask, do you have your own business or do you cut for someone (what would be the correct term?) or . . . ?

WOW - great.

They are on hold as I need to speak to my jeweler when he gets back tomorrow to see if he's o.k. with either for a certain setting I'm trying to fill.

Thanks TONS,

Sonoma

 

[Proteus]

Sonoma,

You''re very welcome! I''m happy that I was able to help you out.

To answer your question: I''m a freelance faceter right now, but I''m working on starting up a custom gem cutting business. I just haven''t had that much free time to get my website finished, but hopefully I''ll have it up before too long.

I believe I''m permitted to put a website link on my signature line once I''m officially in the trade, so keep an eye out for that.