A brilliant is a

diamond Diamond is a Allotropes of carbon, solid form of the element carbon with its atoms arranged in a crystal structure called diamond cubic. Diamond is tasteless, odourless, strong, brittle solid, colourless in pure form, a poor conductor of e ...

or other

gemstone A gemstone (also called a fine gem, jewel, precious stone, semiprecious stone, or simply gem) is a piece of mineral crystal which, when cut or polished, is used to make jewellery, jewelry or other adornments. Certain Rock (geology), rocks (such ...

cut Cut or CUT may refer to: Common uses * The act of cutting, the separation of an object into two through acutely directed force ** A type of wound ** Cut (archaeology), a hole dug in the past ** Cut (clothing), the style or shape of a garment ** ...

in a particular form with 57-58

facet Facets () are flat faces on geometric shapes. The organization of naturally occurring facets was key to early developments in crystallography, since they reflect the underlying symmetry of the crystal structure. Gemstones commonly have facets cu ...

s so as to have exceptional brilliance. The word 'brilliant' is also used for a diamond cut in this fashion. The underside is

conical In geometry, a cone is a three-dimensional figure that tapers smoothly from a flat base (typically a circle) to a point not contained in the base, called the ''apex'' or '' vertex''. A cone is formed by a set of line segments, half-lines, ...

, a shape that provides maximal light return through the top of the diamond. Even with modern techniques, the cutting and polishing of a diamond

crystal A crystal or crystalline solid is a solid material whose constituents (such as atoms, molecules, or ions) are arranged in a highly ordered microscopic structure, forming a crystal lattice that extends in all directions. In addition, macros ...

always results in a dramatic loss of weight; rarely is this loss less than 50%. The round brilliant cut is preferred when the crystal is an

octahedron In geometry, an octahedron (: octahedra or octahedrons) is any polyhedron with eight faces. One special case is the regular octahedron, a Platonic solid composed of eight equilateral triangles, four of which meet at each vertex. Many types of i ...

, as often two stones may be cut from one such crystal. Oddly-shaped crystals such as

macle Macle is a term used in crystallography. It is a crystalline form, twin-crystal or double crystal (such as chiastolite). It is crystallographic twin according to the spinel twin law and is seen in octahedral crystals or minerals such as dia ...

s 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.

Origin and etymology

The earliest diamond cutting techniques were simply to polish the natural shape of

rough diamond A rough diamond is a diamond that has not been cut or processed. They come in a variety of naturally occurring shapes, including octahedral (eight-sided bipyramid), cubic, and triangular (most commonly macles). A raw diamond or rough diamond ...

s, often

octahedral In geometry, an octahedron (: octahedra or octahedrons) is any polyhedron with eight faces. One special case is the regular octahedron, a Platonic solid composed of eight equilateral triangles, four of which meet at each vertex. Many types of i ...

crystals. Around the 1500s, polishing and cutting inventions made it possible to shape diamonds better, cut

s and make the stones sparkle more. By 1750, a round cut called Old European cut had developed. It was improved into the Circular (or Transitional) brilliant around 1880, to be finalized as the modern round brilliant cut in 1950. As brilliant cut diamonds became more popular, the term 'brilliant' transitioned from being just the name of a style to cut a gemstone, to be used as a common name or abbreviation for 'round brilliant cut diamonds'.

Facet proportions and names

The modern round brilliant-cut was developed by Marcel Tolkowsky in 1919. The ideal proportions are 100% diameter, 53% table, 43.1% pavilion and 16.2% crown. The girdle and

culet In gemology, a culet is a flat face on the bottom of a gemstone. During the 14th century, after the adoption of the table cut, a further facet was added to the bottom of the cut parallel to the surface of the table. The term used for these b ...

(if anynot part of Tolkowsky's original design) are cut from the ideal brilliant. The modern round brilliant consists of 58 facets (or 57 if the

is excluded), ordinarily today cut in two pyramids placed base to base: 33 on the ''crown'' (the top half above the middle or ''girdle'' of the stone), truncated comparatively near its base by the table, and 25 on the ''pavilion'' (the lower half below the girdle), which has only the apex cut off to form the culet, around which 8 extra facets are sometimes added. Over time it has become usual for most girdles to be 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 standardised. Some gem cutters refer to an American brilliant cut or a Scandinavian brilliant cut. According to Green et al. 2001: Figures 1 and 2 show the facets of a round brilliant diamond. Figure 1 assumes that the "thick part of the girdle" is the same thickness at all 16 "thick parts". It does not consider the effects of indexed upper girdle facets. Figure 2 is adapted from Figure 37 of Marcel Tolkowsky's ''Diamond Design'', which was originally published in 1919. Since 1919, the lower girdle facets have become longer. As a result, the pavilion main facets have become narrower.

Cut grading

The relationship between the crown angle and the pavilion angle has the greatest effect on the look of the diamond. A slightly steep pavilion angle can sometimes be complemented by a shallower crown angle and ''vice versa''. Other proportions also affect the look of the diamond: * The table ratio is highly significant. * The length of the lower girdle facets affects whether

Hearts and arrows Hearts most commonly refers to: * Hearts (card game), a trick-taking game ** Black Lady, a common variant of Hearts * Hearts (suit), one of the standard four suits of cards * Heart, an organ Hearts may also refer to: Music * The Hearts, an Amer ...

can be seen in the stone, under certain viewers. ** Most round brilliant diamonds have roughly the same girdle thickness at all 16 "thick parts". ** So-called "cheated" girdles have thicker girdles where the main facets touch the girdle than where adjacent upper girdle facets touch the girdle. These stones weigh more for a given diameter, average girdle thickness, crown angle, pavilion angle, and table ratio, and have worse optical performance, i.e., their upper girdle facets appear dark in some lighting conditions. ** So-called "painted" girdles have thinner girdles where the main facets touch the girdle than where adjacent upper girdle facets touch the it. These stones (such as EightStar-brand diamonds) have less light leakage at the edge of the stone (for a given crown angle, pavilion angle, and table ratio). Some diamonds with painted girdles receive lower grades in the GIA's cut grading system, for reasons given in a 2005 GIA article. Several groups have developed diamond cut grading standards. These standards differ somewhat on which proportions make the best cut. There are certain proportions that are considered best by two or more groups, however. * The AGA standards may be the strictest. David Atlas, who developed the AGA standards, has suggested that they are overly strict. * The HCA (Holloway Cut Adviser) changed several times between 2001 and 2004. , an HCA score below two represented an excellent cut. The HCA distinguishes between brilliant, Tolkowsky, and fiery cuts. * The American Gem Society (AGS) standards changed in 2005 in order better to match Tolkowsky's model and Octonus' ray tracing results. The 2005 AGS standards penalize stones with "cheated" girdles. They grade from 0 to 10. *The GIA began grading cut on every grading report beginning in 2006, based on their comprehensive study of 20,000 proportions with 70,000 observations of 2,000 diamonds. The single descriptive words are as follows: Excellent, Very Good, Good, Fair, and Poor. The distance from the viewer's eye to the diamond is important. The 2005 AGS cut standards are based on a distance of 25 centimeters (about 10 inches). The 2004 HCA cut standards are based on a distance of 40 centimeters (about 16 inches). Polish and symmetry are two important aspects of cut. The polish grade describes the smoothness of the diamond's facets and the symmetry grade refers to alignment of the facets. With poor polish, the surface of a facet can be dull and may create blurred or dull sparkle. The stone may look like it needs to be cleaned. Because of the lack of symmetry, light can be misdirected as it enters and exits the diamond.

Hearts and arrows phenomenon

A diamond that has the top facet or "table facet" exactly perpendicular to the bottom of the diamond or "pavilion" and has its other facets precisely aligned with excellent symmetry, may show patterns that look like arrows from the top and hearts from the bottom. Generally it will need to be viewed loose under a gemscope to see the pattern very well. Although the hearts and arrows property is indicative of a top-tier cut, it does not always mean the diamond will be the most brilliant. Optimal facet placement is the key to brilliance and more important than facet patterning. Not all ideal round cuts will have the hearts and arrows effect either.

References

External links