Vintage Ametrine Ring

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Ametrine is a quartz stone that is an Amethyst and Citrine.

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Reference Information on Gem Cuts and Carat Weight gathered from different sources.

Formulas for Various Gem Cuts. It is difficult to figure the carat wt. of a gem that is in a setting.

S.G. (Specific Gravity)
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Round faceted stones: Diameter squared x depth x S.G. x .0018 = carat wt.

Oval faceted stones: Diameter squared x depth x S.G. x .002 = carat wt.

Emerald cut faceted stones: Length x width x depth x S.G. x .0025 = carat wt.

Rectangular faceted stones: Length x width x depth x S.G. x .0026 = carat wt.

Square cut faceted stones: Length x width x depth x S.G. x .0023 = carat wt.

Marquise cut stones, (navette): Length x width x depth x S.G. x .0016 = carat wt.

Pear cut stones: Length x width x depth x S.G. x .00175 = carat wt.

Square cushions:(avg. corner meas.& belly meas. for dia.) Diameter squared x depth x S.G. x .0018 = carat wt.

Rectangular Cushions:(avg. L & W for dia.) Diameter squared x depth x S.G. x .0022 = carat wt.

Square step cut stones:(avg. both meas. for dia.) Diameter squared x depth x S.G. x .0023 = carat wt.

Rectangular step cut stones: Length x width x depth x S.G. x .0025 = carat wt.

Cabochon cut stones: Length x width x depth x S.G. x .0027 = carat wt.

Adjustments:

GIRDLE

Use an average of the girdle thickness. Do not base your reading on a bulge at the top of a heart, or the point of a gem.

Thin girdle, subtract 1% to 2%

Slightly thick, add 1% to 2%

Thick, add 3% to 4%

Very thick, add 5% to 6%

Extra thick, add 7% to 10%

PAVILION BULGE

Slight, add 3% to 5%

Noticeable, add 6% to 8%

Obvious, add 9% to 12%

Extreme, add 13% to 18%

A long culet due to steep pavilion angles can add up to 5%

SHAPE OUTLINE

On cut corner square and rectangle, wide corners can decrease weight as much as 5%.

Oval, pear, marquis, and heart, wide wings or high shoulders can add up to 10%. Occasionally, straight shoulders will require a deduction of 1% to 5%.

Marquis and sometime pears will have a very short keel, or none at all. This will reduce the weight by 1% to 3%.

Triangles with straight sides will require a reduction of up to 10%.

Metric Size Weight Tool |

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