Diamond cut

The practical history of diamond cuts can be traced back to the Middle Ages, while their theoretical basis was not developed until the turn of the 20th century.

The most popular of diamond cuts is the modern round brilliant, whose 57 facets arrangements and proportions have been perfected by both mathematical and empirical analysis.

A diamond's cut is evaluated by trained graders, with higher grades given to stones whose symmetry and proportions most closely match the particular "ideal" used as a benchmark.

In or around 1476, Lodewyk van Bercken, a Flemish polisher of Bruges, introduced the technique of absolute symmetry in the disposition of facets using a device of his own invention, the scaif.

About the middle of the 16th century, the rose or rosette was introduced in Antwerp: it also consisted of triangular facets arranged in a symmetrical radiating pattern, but with the bottom of the stone left flat—essentially a crown without a pavilion.

However, Indian "rose cuts" were far less symmetrical as their cutters had the primary interest of conserving carat weight, due to the divine status of diamond in India.

[8] Around the turn of the century, the development of motorized rotary saws for cutting diamonds, patented in 1901 by John H. G. Stuurman[9] and in 1902 by Ernest G. H. Schenck,[10] gave cutters creative freedom to separate small stones not detachable by cleaving as they wish and allowed them to waste less.

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.

This factor further highlights the need to reevaluate Tolkowsky's results, and to recalculate the effects of a diamond's proportions on its appearance aspects.

Foremost is the refractive index (RI) of a diamond, which, at 2.417 (as measured by sodium light, 589.3 nm), is fairly high compared with that of most other gems.

Also important is a diamond's dispersive power—the ability of the material to split white light into its component spectral colors—which is also relatively high, at 0.044 (as measured from the B-G interval).

Internal brilliance—the percentage of incident light reflected back to the viewer from the rear (pavilion) facets—relies on careful consideration of a cut's interfacial angles as they relate to diamond's RI.

[14] The term scintillation brilliance is applied to the number and arrangement of light reflections from the internal facets; that is, the degree of "sparkle" seen when the stone or observer moves.

One example is grain lines (produced when irregular crystallization occurs as a diamond is formed) running across the facet.

Round brilliants have certain requisite proportions that would result in high weight loss, whereas fancy cuts are typically much more flexible in this regard.

This is because a full-cut brilliant of such small size would appear milky to the human eye, owing to its inability to resolve the stone's dispersive fire.

Conventional round brilliant or fancy cuts do not scale up satisfactorily, so the extra facets are needed to ensure there are no "dead spots".

[16] Simultaneously, giving a fancy diamond cut as a precious jewel on specific celebrations became a part of tradition.

A Heart cut diamond has romantic symbolism, so it is a common gift for Valentine's Day or a wedding anniversary.

The most famous shapes are: Princess, Cushion, Heart, Pear, Marquise, Radiant, Asscher cut, Emerald, Oval.

[24] This is the most populous category of fancy cut, because the standard round brilliant can be effectively modified into a wide range of shapes.

[25] Modern cutting technology has allowed the development of increasingly complex and hitherto unthinkable shapes, such as stars and butterflies.

Their proportions are mostly a matter of personal preference; however, due to their sharp terminations and diamond's relative fragility, these cuts are more vulnerable to accidental breakage and may therefore be more difficult to insure.

[26] There are several older modified brilliant cuts of uncertain age that, while no longer widely used, are notable for history's sake.

The extra care required for these sub-girdle facets benefits the finished stone by mitigating girdle irregularity and bearding (hairline fracturing).

They may resemble the square-shaped Princess cut in passing, but a carré's lack of fire and simpler facets are distinctive.

They have been extremely successful commercially and continue to gain popularity, loosening the foothold of the de facto standard round brilliant.

Invented by South African diamond cutter Basil Watermeyer and named after himself and his wife Marion, the basic Barion cut is an octagonal square or rectangle, with a polished and faceted girdle.

Both it and the Barion cut exist in a large number of modified forms, with slightly different facet arrangements and combinations.

Like the older style brilliants and step cuts, there is a growing demand for the purpose of repairing or reproducing antique pieces.