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Good cut in Gemstone: easy way to understand the basics

To gemstone lovers like ourselves, a good cut is all-important.
The first step in good gem cutting is to cut a colored gemstone with the same precision and parameters as cutting a diamond. However unlike diamonds, each type of colored gemstone varies in their level of hardness, the way they behave optically, and the weight loss suffered applying this technique could be much higher than seen in diamonds.
The essential rule to cutting a colored gemstone is creating symmetrical facets that reflect light evenly across the surface. The light should enter the gemstone from the crown, bounce within the stone, and be reflected back to our eye. This can be achieved by adjusting the inclination of the angles on the crown (the top of the stone) and the pavilion (the bottom of the stone), as shown in the diagram below.

Therefore, on every buying trip, the first thing we do when shopping for colored stones is examine the quality of each stone’s cut. We look for gemstones that have a minimal ‘window’ or see-through effect, which is a clear indicator of poor cutting. The easiest way to test a gemstone for poor cutting is to place the gemstone face up on your hand and see how clearly you can see your hand through the center of the stone. The less you can see-through the center of the stone, the better that gemstone is cut. This is quick, but ever-important, test to apply before we buy any stone because it is one of the main factors that helps us determine the estimated weight loss we will incur if we decide to recut it for perfection.
In the case of the exquisite mint tourmaline stone shown below, you can see the stone has an outstanding brightness over the entire surface and you cannot see my hand, in the slightest, through the stone. This proves the stone was cut with precision.
The second, but equally as fundamental, step in evaluating a gemstone’s cut, is to look at the gemstone in a dark environment and assess the level of ‘returned light’ or its’ brightness. The brighter a stone can appear in the dark, the higher quality of the gemstone’s cut. Since it’s not realistic to always purchase gemstones during the night or to control overhead lights, we test stones by looking at them on our hand underneath a table. 
With over thirty years experience traveling the globe in search for rare materials, it has become second nature to inspect a gemstone’s cut at first glance. That is why you will see the characteristics we described through out the Paolo Costagli collection.



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