How To Buy Gemstones page 8 of 10
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Cut Last but not least is the quality of the stone’s cut. The entire purpose of the cutting process is to optimize the stone’s reflection of light, and so enhance its luster and brilliance. There are four major factors that determine the quality of a cut gemstone. Proportions, Shape, Faceting and Polish.
When cutting a gemstone, the piece is divided to two: side A and side B, which are also called “crown” and “pavilion”. These are divided by the girdle: the thin round line that surrounds the stone in its widest section.
The respective height of each side, in comparison with the total height of the stone is called the proportion. If one of the sides (or both) is either too flat or too high, it will reduce the effect of the refractive light and will result in less brilliance. Bad proportions also cause various ugly effects, the most notorious of which is the “window”. When looking top-down at a badly cut stone, one which has wrong proportions, you can see that the main part of it is actually transparent, so that you can look through as if it were a window. This is easy to spot, and when you do, you know you are looking at a poor cut.
The exact proportions for maximum brilliance have been calculated very accurately way in diamonds, and most diamonds nowadays are cut by a machine that keeps to these proportion perfectly. In gemstones the calculations are approximate, and most of the cutting is still by hand.
When searching for gemstones, you will often find stones with bad proportions. This is because the natural tendency of the cutter is to get high yield from the raw material he buys. Keeping perfect proportions involves a greater loss of material during the cutting process, so many cutters prefer to mis-cut the stone (and produce a fat pavilion, or, in case of flat rough-stone, very flat sides), rather than reducing its weight or size. By doing this, they can of course offer the stone at a lower price from what it would have fetched had it been cut to perfect proportions. But remember that there is a downside: you are in effect paying for extra weight that shouldn’t be there, and that actually damages the overall look of the stone.
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Find more info in our gemstones articles section.