Diamond Cut
The history of diamond cutting can be traced to the late Middle Ages, before which time diamonds were enjoyed in their natural octahedral state. The first "improvements" on nature's design involved a polishing of the crystal faces—this was called the point cut. Later still, a little less than one half of the crystal would be sawn off, creating the table cut. Neither of these early cuts would reveal what diamond is prized for today; its strong dispersion or fire. At the time, diamond was valued chiefly for its brilliant lustre and superlative hardness; a table-cut diamond would appear black to the eye, as they do in paintings of the era.
After 1676 the rose cut came into use by Belgian cutters: this was the first truly multi-faceted cut, with upwards of 16 facets. It is likely the rose cut is a design adopted from India, as many of the historical Indian diamonds were fashioned in this manner (although less symmetrically, as Indian cutters sought to minimize wastage).
Roughly 1900, the development of diamond saws and good jewellery lathes enabled the development of modern diamond cuts, chief among them the round brilliant cut. In 1919, Marcel Tolkowsky analyzed this cut. His calculations took both brilliance (the amount of white light reflected) and fire into consideration, creating a delicate balance between the two. His geometric calculations can be found in his book on Diamond Design (http://www.folds.net/diamond/index.html).
The modern round brilliant consists of 58 facets (or 57 if the culet is excluded); 33 on the crown (the top half above the middle or girdle of the stone) and 25 on the pavilion (the lower half below the girdle). In recent decades, most girdles are faceted. Many girdles have 32, 64, 80, or 96 facets; these facets are not counted in the total. While the facet count is standard, the actual proportions (crown height and angle, pavilion depth, etc.) are not universally agreed upon. One may speak of the American cut or the Scandinavian standard (Scan. D.N.), to give but two examples.
Even with modern techniques, the cutting and polishing of a diamond crystal always results in a dramatic loss of weight; rarely is it less than 50%. The round brilliant cut is preferred when the crystal is an octahedron, as often two stones may be cut from one such crystal. Oddly shaped crystals such as macles are more likely to be cut in a fancy cut—that is, a cut other than the round brilliant—which the particular crystal shape lends itself to.
Popular fancy cuts include the baguette (from the French, resembling a loaf of bread), marquise or navette ("little boat"), princess (square outline), heart, briolette (a form of the rose cut), and the pear or drop cuts. Generally speaking, these "fancy cuts" are not held to the same strict standards as Tolkowsky-derived round brilliants. Cuts are influenced heavily by fashion; baguettes—which accentuate a diamond's lustre and downplay its fire—were all the rage during the Art Deco period, whereas the princess cut—which accentuates a diamond's fire rather than its lustre—is currently gaining popularity. The princess cut is also popular amongst diamond cutters: of all the cuts, it wastes the least of the original crystal.
In the 1970s, Bruce Harding developed another mathematical model for gem design. Since then, several groups have used computer models GIA, and folds.net and specialized scopes to design diamond cuts.
During the 1990s Israeli interests acquired about 20% of the diamond trade, buying diamonds from Russia and from mines in Africa not controlled by De Beers. De Beers now deals only in diamonds from their own mines. A major diamond cutting industry has grown up in Gujarat State, India where 90% of the world's diamonds (as measured by number of diamonds) are cut by a workforce of 800,000 [2] (http://www.vibrantgujarat.com/sp-gems.html). Small diamonds previously not worth cutting are cut in India, opening up a new market segment for small diamonds.
Some cuts are:
- Round
- Radiant
- Pear
- Marquise
- Emerald
- Oval
- Heart
- Princess
The choice of cut is often decided by the original shape of the rough stone, location of the inclusions and flaws to be eliminated, the preservation of the weight, popularity of certain shapes amongst consumers and many other considerations. As far as the shape of the cut is concerned, it is very much a personal taste and preference. However, when jewelers judge the quality of a cut diamond, they often rate "Cut" as the most important of the "4-Cs." The key is not about the shape, but how good a job the cutters executed for a given shape. The proportion, symmetry and quality of the polish are essential criteria of a good cut. Since the "brilliance" and "fire" of a diamond depends very much on the angle of the facets in relation to each other. A poorly cut diamond with facets cut only a few degrees from optimal will result in a stone that lacks the gem quality. For a round brilliant cut, there is a balance between "brilliance" and "fire". When a diamond is cut for too much "fire", it would look like a cubic zirconia which gives out much more "fire" than real diamond. A well executed round brilliant cut should reflect most light out from the tabletop and make the diamond appear white when viewed from the top. An inferior cut will produce a stone that appears dark at the center and in some extreme cases the ring settings may show through the top of the diamond as shadows.
Sometimes the cutters compromise and accept lesser proportions and symmetry in order to avoid inclusions or to preserve the carat rating. Since the per-carat price of diamond is much higher when the stone is over one carat, many one-carat diamonds are the result of compromising "Cut" for "Carat". Some jewelry experts advise consumers to buy a .99 carat diamond for its better price or buy a 1.10 carat diamond for its better cut. A 1.00 carat diamond is usually poorly cut stone.
The "Cut" of the "4-Cs" is the most difficult part for a consumer to choose in selecting a good diamond because a GIA certificate will only show the measurements without a subjective ranking of how good the cut was. The other 3-Cs can be ranked simply by the rating in each category. It requires a trained eye to see the quality of a good "cut".