Brilliant Crystal Jewelry
Q.I've been shopping around the diamond district in NYC and I found a stone that "looked" pretty nice -- its a round brilliant 1.00 ct, F-VS2. According to the GIA certificate, all of the dimensions on the stone seem good except for the most important -- Depth. It had a 65 depth. Does that mean that it just looks smaller? Can anyone please comment on the value of a diamond with this particular cut?
A.In modern round brilliant cut diamonds larger than melee sizes, this is not very common, as most round brilliants are cut from a roughly pyramid shaped piece of rough (half the octahedral crystal) which is usually slightly steeper angled than needed for correct pavilion angles. Thus it's far more common to see pavilion angles that are too deep, than too shallow. Those distorted crystals which might tend to produce fisheye proportions are more often cut into fancy shapes, so as to avoid that problem. But you DO see the fisheye look in some of the old european cut stones, and in occasional melee diamonds. As the pavilion angles get too deep (above about 43 to 44 percent), the table reflection gets darker, and larger. As this effect increases, the diamond starts to look more like a donut, with a brilliant periphery, and a mostly non-brilliant dark area filling up the table region. If this is so extreme as to really just look like a black table area (sometimes extending to the star facets as well), then it's nicknamed a "nailhead". While this degree of deep pavilion, like the fisheye degree of shallow pavilion, is not very common (The stones are quite ugly and hard to sell, so few cutters push the limits that far), an intermediate range of deep pavilion is quite common. More so, in fact, than truly well cut stones. Learning to look for the table reflection in a round brilliant is fairly easy to do, and a very quick check on the pavilion proportions. In a well cut stone, it's a generally circular area in the center of the table, about one third the size of the table. At that size, it's more just a hazy zone in the center, rather than appreciably darker than the rest of the pavilion. As the pavilion gets deeper, that reflection gets larger and darker. If it's much larger than about half the size of the table, then it starts to become a noticable hole in the brilliance of the diamond, and at that point one should pass on the stone for another diamond if one is looking for a well cut diamond. Note that this need only be a purely visual inspection. You don't need the numbers, though of course this method is also a good way of visually measuring the pavilion depth percentage. But if you know (from a certificate, for example) the total depth percentage, and the table percentage, you have almost enough information to judge the diamonds cut. Checking the pavilion depth as I've described is all that's required to verify that what seems, from the numbers, to be a well cut diamond, is in fact what it seems. If it's acceptable, and the other measurements you already have are also acceptable, then the somewhat harder to measure crown angles or height will also be about right.
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