Trillion Shape - Plain Cut

In the gemstone world we are taught that shape and cut are different concepts. But the difference isn't always obvious. Is a trillion a cut or a shape? The term cushion cut clearly suggests it refers to a cut. But the word cushion is a shape term -- it means shaped like a cushion or pillow. The same goes for pear. It seems obvious that it's a shape. So why do we say pear-cut when we refer to a gemstone in the shape of a pear? It all sounds rather confusing. Maybe trying to distinguish between shape and cut is not such a good idea after all.

Round Shape - Portuguese Cut

Even if our everyday speech is a little loose, there actually is a point to the distinction between shape and cut. Understanding the difference between shape and cut helps us understand what gem cutting is all about. So let's see if we can make sense out of the confusion.

Cushion Shape - Facet Cut

Consider round gemstones. Looking at our inventory of round shape gems, we find a number of different round stones: some are cut as cabochons, with no facets at all. Some are faceted in the traditional way, in the so-called brilliant cut. Yet others are cut with a very different faceting technique, called the concave cut. Yet others have what is called the portuguese cut.

So we have one shape -- round -- and multiple cutting styles. Though we sometimes use the phrase round-cut, it's obvious from our example that this phrase doesn't make a lot of sense. We need to say round portuguese cut or round cabochon, and so on.

Oval and Pear Shape - Cabochon Cuts

The meaning of the concept of shape should now be fairly obvious. A shape is the face-up outline form of the stone, whether it be round, oval, square, rectangular, pear, marquise or trillion. Given a stone of a certain shape, a gem cutter or lapidary can decide to cut that gem with different styles of facets, or no facets at all.

At the simplest level, we can distinguish the plain cut from the faceted cut. A plain cut has no facets, and may be executed as a level tablet (as in agate) or with a domed top like a cabochon. A faceted cut has a number of separate small planes. There are also mixed cuts which combines the two; for example, a gem with a faceted pavilion and a plain crown.

Round Shape - Brilliant Cut

There are many different facet cuts, but they can be distinguished according to the shape of the facets. There are three basic types: brilliant cuts, with mainly rhomboid and triangular facets in a radial pattern; step cuts with trapezoid or rectangular facets in concentric rows; and mixed cuts combining both brilliant and step-type facets. A detailed description of the various facet cuts can get quite complicated and technical. There are at least six well-known variations on the 56 facet brilliant cut, with different proportions for the facets. Then there are variations on the brilliant cut, with additional facets.

First Published: February-13-2008

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