Cut question for colored gems

[Brightshiny]

I'm interested in another colored stone ring - probably spinel, sapphire, or tourmaline, and I seem to recall reading somewhere that colored stones are usually cut differently than diamonds - they're often deeper and sometimes require specialized settings.

So, what should I know about gemstone cuts for colored stones?

If I'm looking for a relatively shallow cut that will give good finger coverage with a low setting, am I limited to portrait cuts? those don't have great color and can be hard to find. What else can I obsessively stalk look for online?

 

[Autumn in New England]

Yes, colored stones are cut to maximize weight retention, while diamonds are cut for brilliance. So with CS, you often have a lot of bulk in the cut. As such, cut quality matters. You may want to avoid overly deep stones to optimize spread, but shallow stones can negatively affect sparkle and color. So choose wisely. With regard to shape, those that appear larger are round, pear, trilliant, marquise, and oval. Shapes that require more weight in the pavilion (and may therefore look smaller) are princess, asscher, emerald, radiant, and cushion. Specific gravity (density) of the gem also matters. Out of the stones you mentioned, tourmaline is least dense, so it will appear larger than denser gems at the same weight. Spinel is next, and then sapphire is most dense of the 3. Hope this helps!

 

[Avondale]

With a diamond all things regarding cut are a lot more... standardised, I guess, you could say. Angles and ratios are optimised, and it's all numbers.

With coloured stones you judge by eye. Heavy bottoms are common, and often times many compromises are being made for weight retention purposes. But unless you're going for a precision cut, there isn't much optimisation involved in a well cut coloured stone. At least, not in the sense of how it's done with diamonds.

Things I personally look out for:
- does it have a window?
- does it have shadowing/extinction?
- is the pavilion well centred?
- is colour zoning well hidden (if present)?
- does it look pretty overall?

If I'm looking for a relatively shallow cut that will give good finger coverage with a low setting, am I limited to portrait cuts?

Not in the slightest, you'll have an abundance of windowed stones to choose from. It's not the most enticing prospect, I know. In the end you decide which compromises you're okay with and which are deal breakers.

 

[Rfisher]

colored stones are usually cut differently than diamonds - they're often deeper and sometimes require specialized settings.

If it’s customized settings for colored stones you are looking to avoid -
Along with deep belly stones, you’ll also want to be aware of and to be on the lookout for overly thick girdles, wavy gravy girdles or girdles that are not on the same plane as the table facet. Some will be incredibly difficult to impossible to set, and look straight once in the mounting. Or if the stone looks straight - then the setting looks wonky.
The shapes aren’t calibrated so not all ovals, pears and such have the same footprint shape - so the calibrated shape of the stock mounting wouldn’t follow the outlines of the stone.
Of course you can find versions with slight deviations to extremes - how much they bother you to your eye is key.

Happy hunting!

 

[PrecisionGem]

Bad cutting aside, there is a reason that a properly cut colored stone will be deeper than a diamond, and has to do with the refractive index of the gemstone. Each type of gem has a different index. This a measurement of how light is bent as it travels through the stone. Higher numbers bend the light more, and require a more shallow angle. Here is a model of a gem, same cut, but 3 different materials. A brilliant stone allows light to enter through the crown, then bounce back out. If it is not cut correctly, then the light ray enters the crown and doesn't reflect back out, this causes a window. In this case both the Quartz and Tourmaline would show a window, while the diamond material would not.

First the Tourmaline - Refractive Index 1.62
Then Quartz - Refractive index 1.54
Last is the Diamond - Refractive index 2.42

 

[0-0-0]

Some fantasy cuts can be quite shallow and face up large for the carat weight without obvious windows.

 

[Autumn in New England]

Some fantasy cuts can be quite shallow and face up large for the carat weight without obvious windows.

Yes! Concave cuts are notoriously spready.