   #copyright

Diamond cut

2007 Schools Wikipedia Selection. Related subjects: Materials science

   In order to best utilize a diamond gemstone's superlative material
   properties, a number of different diamond cuts have been developed. A
   diamond cut constitutes a more or less symmetrical arrangement of
   facets which together modify the shape and appearance of a diamond
   crystal. Diamond cutters must consider several factors, such as the
   shape and size of the crystal, when choosing a 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. Design creation and innovation continue to the present day:
   new technology—notably laser cutting and computer-aided design—has
   enabled the development of cuts whose complexity, optical performance,
   and waste reduction were hitherto unthinkable.

   The most popular of diamond cuts is the modern round brilliant, whose
   facet arrangements and proportions have been perfected by both
   mathematical and empirical analysis. Also popular are the fancy cuts
   which come in a variety of shapes—many of which were derived from the
   round brilliant. 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. The strictest
   standards are applied to the round brilliant; although its facet count
   is invariable, its proportions are not. Different countries base their
   cut grading on different ideals: one may speak of the American Standard
   or the Scandinavian Standard (Scan. D.N.), to give but two examples.

History

   Diagram of old diamond cuts showing their evolution from the most
   primitive (point cut) to the most advanced pre-Tolkowsky cut (old
   European).The rose cut is omitted, but it could be considered
   intermediate between the old single and Mazarin cuts.
   Enlarge
   Diagram of old diamond cuts showing their evolution from the most
   primitive (point cut) to the most advanced pre-Tolkowsky cut (old
   European).The rose cut is omitted, but it could be considered
   intermediate between the old single and Mazarin cuts.

   The history of diamond cuts can be traced to the late Middle Ages,
   before which time diamonds were enjoyed in their natural octahedral
   state—anhedral (poorly formed) diamonds simply were not used in
   jewellery. The first "improvements" on nature's design involved a
   simple polishing of the octahedral crystal faces to create even and
   unblemished facets, or to fashion the desired octahedral shape out of
   an otherwise unappealing piece of rough. This was called the point cut
   and dates from the mid 14th century; by 1375 there was a guild of
   diamond polishers at Nürnberg. By the mid 15th century, the point cut
   began to be improved upon: a little less than one half of the
   octahedron would be sawn off, creating the table cut. The importance of
   a culet was also realised, and some table-cut stones may possess one.
   The addition of four corner facets created the old single cut (or old
   eight 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 adamantine lustre and superlative hardness;
   a table-cut diamond would appear black to the eye, as they do in
   paintings of the era. For this reason, colored gemstones such as ruby
   and sapphire were far more popular in jewelry of the era.

   In or around 1476, Lodewyk (Louis) van Berquem, a Flemish polisher of
   Bruges, introduced absolute symmetry in the disposition of facets. He
   cut stones in the shape known as pendeloque or briolette; these were
   pear-shaped with triangular facets on both sides. 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. Many large, famous Indian diamonds of old (such as
   the Orloff and Sancy) also feature a rose-like cut; there is some
   suggestion that Western cutters were influenced by Indian stones,
   because some of these diamonds may predate the Western adoption of the
   rose cut. 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. In either event, the rose cut
   continued to evolve, with its depth, number and arrangements of facets
   being tweaked.

   The first brilliant cuts were introduced in the middle of the 17th
   century. Known as Mazarins, they had 17 facets on the crown (upper
   half). They are also called double-cut brilliants as they are seen as a
   step up from old single cuts. Vincent Peruzzi, a Venetian polisher,
   later increased the number of crown facets from 17 to 33 (triple-cut or
   Peruzzi brilliants), thereby significantly increasing the fire and
   brilliance of the cut gem, properties which in the Mazarin were already
   incomparably better than in the rose. Yet Peruzzi-cut diamonds, when
   seen nowadays, seem exceedingly dull compared to modern-cut brilliants.
   Because the practice of bruting (see diamond cutting) had not yet been
   developed, these early brilliants were all rounded squares or
   rectangles in cross-section (rather than circular). Given the general
   name of cushion—what are known today as old mine cuts—these were common
   by the early 18th century. Sometime later the old European cut was
   developed, which had a shallower pavilion, more rounded shape, and
   different arrangement of facets. The old European cut was the
   forerunner of modern brilliants and was the most advanced in use during
   the 19th century.

   Around 1900, the development of diamond saws and good jewelry lathes
   enabled the development of modern diamond cutting and 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 . Tolkowsky's calculations would serve as the
   basis for all future brilliant cut modifications and standards.

   These days many people have overused Tolkowsky's "ideal" model. The
   original model served as a general guideline, as there were several
   aspects of diamond cut that were not explored or accounted for in the
   original model. See excerpts from the GIA article "What did Marcel
   Tolkowsky really say?"

   "Because every facet has the potential to change a light ray's plane of
   travel, every facet must be considered in any complete calculation of
   light paths. Just as a two-dimensional slice of a diamond provides
   incomplete information about the three-dimensional nature of light
   behavior inside a diamond, this two-dimensional slice also provides
   incomplete information about light behaviour outside the diamond. A
   diamond's panorama is three-dimensional. Although diamonds are highly
   symmetrical, light can enter a diamond from many directions and many
   angles. 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.

   Another important point to consider is that Tolkowsky did not follow
   the path of a ray that was reflected more than twice in the diamond.
   However, we now know that a diamond's appearance is composed of many
   light paths that reflect considerably more than two times within that
   diamond. Once again, we can see that Tolkowsky's predictions are
   helpful in explaining optimal diamond performance, but they are
   incomplete by today's technological standards." Even Tolkowsky's
   guidelines should be carefully used only as guidelines as opposed to a
   definitive answer for determining the proportions of a round brilliant
   cut diamond.

   In the 1970s, Bruce Harding developed another mathematical model for
   gem design. Since then, several groups have used computer models (e.g.,
   MSU, OctoNus, GIA, and folds.net) and specialized scopes to design
   diamond cuts.

   The world's top diamond cutting and polishing centre is India. It
   processes 11 out of 12 diamonds in jewellery worldwide. The sector
   employs 1.3 million people and accounts for 14% of India's $80 billion
   of annual exports. Its share in the world polished diamond market is
   92% by pieces and 55% by value.

Theory

   In its rough state, a diamond is fairly unremarkable in appearance.
   Most gem diamonds are recovered from secondary or alluvial deposits,
   and such diamonds have dull, battered external surfaces often covered
   by a gummy, opaque skin—a comparison to "lumps of washing soda" is apt.
   The act of polishing a diamond and creating flat facets in symmetrical
   arrangement brings out the diamond's hidden beauty in dramatic fashion.

   When designing a diamond cut, two primary factors are considered.
   Foremost is the refractive index (RI) of diamond, which, at 2.417 (as
   measured by sodium light, 589.3 nm), is fairly high compared with that
   of most other gems. Diamond's RI is responsible for its brilliance—the
   amount of incident light reflected back to the viewer. Also important
   is 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). The flashes of
   spectral colors—known as fire—are a function of this dispersion, but
   are, like brilliance, only apparent after cutting.

   Brilliance can be divided into the definitions external brilliance and
   internal brilliance. The former is the light reflected from the surface
   of the stone—its luster. Diamond's adamantine ("diamond-like") luster
   is second only to metallic (i.e., that of metals); while it is directly
   related to RI, the quality of a finished stone's polish will determine
   how well a diamond's luster is borne out.

   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. The goal is to attain total internal reflection (TIR) by choosing
   the crown angle and pavilion angle (the angle formed by the pavilion
   facets and girdle plane) such the reflected light's angle of incidence
   (when reaching the pavilion facets) falls outside diamond's critical
   angle, or minimum angle for TIR, of 24.4°. Two observations can be
   made: if the pavilion is too shallow, light meets the pavilion facets
   within the critical angle, and is refracted (i.e., lost) through the
   pavilion bottom into the air. If the pavilion is too deep, light is
   initially reflected outside the critical angle on one side of the
   pavilion, but meets the opposite side within the critical angle and is
   then refracted out the side of the stone.

   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.
   Scintillation is dependent on the size, number, and symmetry of facets,
   as well as on quality of polish. Very small stones will appear milky if
   their scintillation is too great (due to the limitations of the human
   eye), whereas larger stones will appear lifeless if their facets are
   too large or too few.

   A diamond's fire is determined by the cut's crown height and crown
   angle (the crown being the top half of the stone, above the girdle),
   and the size and number of facets that compose it. The crown acts as a
   prism: light exiting the stone (after reflection from the pavilion
   facets) should meet the crown facets at as great an angle of incidence
   from the normal as possible (without exceeding the critical angle) in
   order to achieve the greatest fanning out or spread of spectral colors.
   The crown height is related to the crown angle, the crown facet size,
   and the table size (the largest central facet of the crown): a happy
   medium is sought in a table that is not too small (which would result
   in larger crown facets and greater fire at the expense of brilliance)
   or too large (which would result in smaller crown facets and little to
   no fire).

Choice of cut

   The choice of diamond cut is often decided by the original shape of the
   rough stone, location of internal flaws or inclusions, the preservation
   of carat weight, and popularity of certain shapes amongst consumers.
   The cutter must consider each of these variables before proceeding.

   Most gem-quality diamond crystals are octahedrons in their rough state
   (see material properties of diamond). These crystals are usually cut
   into round brilliants because it is possible to cut two such stones out
   of one octahedron with minimal loss of weight. If the crystal is
   malformed or twinned, or if inclusions are present at inopportune
   locations, the diamond is more likely to receive a fancy cut (a cut
   other than a round brilliant). This is especially true in the case of
   macles, which are flattened twin octahedron crystals. Round brilliants
   have certain requisite proportions which would result in high weight
   loss, whereas fancy cuts are typically much more flexible in this
   regard. Sometimes the cutters compromise and accept lesser proportions
   and symmetry in order to avoid inclusions or to preserve carat weight,
   since the per-carat price of diamond is much higher when the stone is
   over one carat (200 mg).

   While the round brilliant cut is considered standard for diamond, with
   its shape and proportions nearly constant, the choice of fancy cut is
   influenced heavily by fashion. For example, the step cut baguette—which
   accentuates a diamond's luster, whiteness, and clarity but downplays
   its fire—was all the rage during the Art Deco period, whereas the mixed
   Princess cut—which accentuates a diamond's fire and brilliance rather
   than its luster—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. Older diamonds cut before ca. 1900 were
   cut in "primitive" versions of the modern round brilliant, such as the
   rose cut and old mine cut (see History section). Although there is a
   market for antique stones, many are recut into modern brilliants to
   increase their marketability. There is also increasing demand for
   diamonds to be cut in older styles for the purpose of repairing or
   reproducing antique jewelry.

   The size of a diamond may also be a factor. Very small (< 0.02 carats
   (4 mg)) diamonds—known as melée—are usually given simplified cuts
   (i.e., with fewer facets). 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. Conversely, very large diamonds
   are usually given fancy cuts with many extra facets. Conventional round
   brilliant or fancy cuts do not scale up satisfactorily, so the extra
   facets are needed to ensure there are no "dead spots". Because large
   diamonds are less likely to be set in jewelry, their cuts are
   considered for how well they display the diamonds' properties from a
   wide range of viewing directions; in the case of more moderate-sized
   diamonds, the cuts are considered primarily for their face-up appeal.

Round brilliant

   Developed ca. 1900, the round brilliant is the most popular cut given
   to diamond. It is usually the best choice in terms of saleability,
   insurability (due to its relatively "safe" shape), and desired optics.

Facet count and names

   Diamond proportions and facets, for the round brilliant cut.

   The modern round brilliant (Figure 1 and 2) 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). The girdle may be frosted, polished smooth, or
   faceted. In recent decades, most girdles are faceted; many have 32, 64,
   80, or 96 facets ( People's Diamonds has a distinctive 100 facet cut;
   these facets are excluded from the total facet count. Likewise, some
   diamonds may have a number of small extra facets on the crown or
   pavilion that were created to remove surface imperfections during the
   diamond cutting process. Depending on their size and location, they may
   negatively impact the symmetry of the cut and are therefore considered
   during cut grading.

   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.

Proportions

   While the facet count is standard, the actual proportions—crown height
   and crown angle, pavilion depth and pavilion angle, and table size—are
   not universally agreed upon. There are at least six "ideal cuts" that
   have been devised over the years, but only three are in common use as a
   means of benchmarking. Developed by Marcel Tolkowsky in 1919, the
   American Standard (also known as the American Ideal and Tolkowsky
   Brilliant) is the benchmark in North America. It was derived from
   mathematical calculations that considered both brilliance and fire. The
   benchmark in Germany and other European countries is the Practical Fine
   Cut (German: Feinschliff der Praxis, also known as the Eppler Cut),
   introduced in 1939. It was developed in Germany by empirical
   observations and differs only slightly from the American Standard.
   Introduced as part of the Scandinavian Diamond Nomenclature (Scan. D.
   N.) in 1969, the Scandinavian Standard also differs very little.

   Other benchmarks include: the Ideal Brilliant (developed in 1929 by
   Johnson and Roesch); the Parker Brilliant ( 1951); and the Eulitz
   Brilliant ( 1972). The Ideal and Parker brilliants are disused because
   their proportions result in (by contemporary standards) an unacceptably
   low brilliance. The Eulitz cut is the only other mathematically-derived
   benchmark; it is also the only benchmark to consider girdle thickness.
   A summary of the different benchmarks is given below:
   Benchmark Crown height Pavilion depth Table diameter Girdle thickness
   Crown angle Pavilion angle
   American Standard 16.2% 43.1% 53.0% N/A 34.5° 40.75°
   Practical Fine Cut 14.4% 43.2% 56.0% N/A 33.2° 40.8°
   Scandinavian Standard 14.6% 43.1% 57.5% N/A 34.5° 40.75°
   Eulitz Brilliant 14.45% 43.15% 56.5% 1.5% 33.36° 40.48°
   Ideal Brilliant 19.2% 40.0% 56.1% N/A 41.1° 38.7°
   Parker Brilliant 10.5% 43.4% 55.9% N/A 25.5° 40.9°

   Crown height, pavilion depth, and table diameter are percentages of the
   total girdle diameter. Because the pavilion angle (and consequently
   pavilion depth) is so closely tied to total internal reflection, it
   varies the least between the different standards.

Fancy cuts

   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. The prevalence and choice of a
   particular fancy cut is also influenced by fashion; generally speaking,
   these cuts are not held to the same strict standards as
   Tolkowsky-derived round brilliants. Most fancy cuts can be grouped into
   four categories: modified brilliants, step cuts, mixed cuts, and rose
   cuts.

Modified brilliants

   This is the most populous category of fancy cut, because the standard
   round brilliant can be effectively modified into a wide range of
   shapes. Because their facet counts and facet arrangements are the same,
   modified brilliants also look (in terms of brilliance and fire
   interplay) the most like round brilliants and are therefore (in general
   and at present) the most saleable. Certain modified round brilliants
   also exhibit better Diamond Light Performance

   Modified brilliants include the marquise or navette (French for "little
   boat", because it resembles the hull of a sailboat), heart, triangular
   trillion (also trillian or trilliant), oval, and the pear or drop cuts.
   These are the most commonly encountered modified brilliants; 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.

   There are several older modified brilliant cuts of uncertain age that,
   while no longer widely used, are notable for history's sake. They are
   all round in outline and modify the standard round brilliant by adding
   facets and changing symmetry, either by dividing the standard facets or
   by placing new ones in different arrangements. These cuts include: the
   King and Magna cut, both developed by New York City firms, with the
   former possessing 86 facets and 12-fold symmetry and the latter with
   102 facets and 10-fold symmetry; the High-Light cut, developed by
   Belgian cutter M. Westreich, with 16 additional facets divided equally
   between the crown and pavilion; and the Princess 144, introduced in the
   1960s, with 144 facets and 8-fold symmetry. Not to be confused with the
   mixed Princess cut, the Princess 144 cut makes for a lively stone with
   good scintillation; the extra facets are cut under the girdle rather
   than subdivided. The extra care required for these sub-girdle facets
   benefits the finished stone by mitigating girdle irregularity and
   bearding (hairline fracturing). Today, with increase understanding of
   light dynamics and diamond cutting, many companies have developed new
   modified round brilliant cut diamonds. If designed correctly these
   extra facets of the modified round brilliant could benefit the over
   beauty of a diamond, such as in 91 facet diamonds. Especially with in
   the movement toward Diamond Light Performance.

Step cuts

   Stones whose outlines are either square or rectangular and whose facets
   are rectilinear and arranged parallel to the girdle are known as step-
   or trap-cut stones. These stones often have their corners truncated,
   creating an emerald cut (after its most common application to emerald
   gemstones) with an octagonal outline. This is done because sharp
   corners are points of weakness where a diamond may cleave or fracture.
   Instead of a culet, step-cut stones have a keel running the length of
   the pavilion terminus. Because both the pavilion and crown are
   comparatively shallow, step cut stones are generally not as bright and
   never as fiery as brilliant cut stones, but rather accentuate a
   diamond's clarity (as even the slightest flaw would be highly visible),
   whiteness, and lustre (and therefore good polish).

   Due to the current vogue for brilliant and brilliant-like cuts, step
   cut diamonds may suffer somewhat in value; stones that are deep enough
   may be re-cut into more popular shapes. However, the step cut's
   rectilinear form was very popular in the Art Deco period. Antique
   jewelry of the period features step-cut stones prominently, and there
   is a market in producing new step-cut stones to repair antique jewelry
   or to reproduce it. The slender, rectangular baguette (from the French,
   resembling a loaf of bread) was and is the most common form of the step
   cut: today, it is most often used as an accent stone to flank a ring's
   larger central (and usually brilliant-cut) stone.

   Square step cuts whose corners are not truncated are known as carré;
   they are also characteristic of antique jewelry. They may resemble the
   square-shaped Princess cut in passing, but a carré's lack of fire and
   simpler facets are distinctive. They may or may not have a culet. In
   Western jewelry dating to before the advent of brilliant-type cuts,
   very shallow step-cut stones were used as lustrous covers for miniature
   paintings: these are known in the antique trade as portrait stones.
   Characteristic of Indian jewelry are lasque diamonds, which may be the
   earliest form of step cut. They are flat stones with large tables and
   asymmetric outlines.

   Other forms of the step cut include triangle, kite, lozenge, trapeze
   (or trapezoid), and obus.

Mixed cuts

   Mixed cuts share aspects of both (modified) brilliant and step cuts:
   they are meant to combine the weight preservation and dimensions of
   step cuts with the optical effects of brilliants. Typically the crown
   is step-cut and the pavilion brilliant-cut. Mixed cuts are all
   relatively new, with the oldest dating back to the 1960s. They have
   been extremely successful commercially and continue to gain popularity,
   loosening the foothold of the de facto standard round brilliant.

   Among the first mixed cuts was the Barion cut, introduced in 1971.
   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. The total
   facet count is 62 (excluding the culet): 25 on the crown; 29 on the
   pavilion; and 8 on the girdle. This cut can be easily identified by the
   characteristic central cross pattern (as seen through the table)
   created by the pavilion facets, as well as by the crescent-shaped
   facets on the pavilion. A similar cut is the Radiant cut: It differs in
   having a total of 70 facets. Both it and the Barion cut exist in a
   large number of modified forms, with slightly different facet
   arrangements and combinations.

   The most successful mixed cut is the Princess cut, first introduced in
   1960 by A. Nagy of London. It was originally intended for flat rough
   (macles), but has since become popular enough that some gemological
   labs, such as that of the American Gem Society (AGS), have developed
   Princess cut grading standards with stringency akin to standards
   applied to round brilliants. Its higher fire and brilliance compared to
   other mixed cuts is one reason for the Princess cut's popularity, but
   more importantly is the fact that, of all the diamond cuts, it wastes
   the least of the original crystal. Another beautiful cut is the
   Flanders cut, a modified square with cut corners, brilliant facets and
   is currently being cut by cutters at Russian Star.

Rose cuts

   Various forms of the rose cut have been in use since the mid 16th
   century. Like the step cuts, they were derived from older types of cuts
   (see History section). The basic rose cut has a flat base (no pavilion)
   and a crown composed of triangular facets (usually 12 or 24) in
   symmetrical arrangement, which rise to form a point. They are usually
   circular in outline; variations include: the briolette (oval); Antwerp
   rose (hexagonal); and double Dutch rose (resembling two rose cuts
   united back-to-back).

   Rose cuts are seldom seen nowadays, except in antique jewelry. Like the
   older style brilliants and step cuts, there is a growing demand for
   rose cuts for the purpose of repairing or reproducing antique pieces.
   The rose cut is still routinely used for melée diamonds.

Cut grading

   The "Cut" of the "4-Cs" is the most difficult part for a consumer to
   judge when selecting a good diamond. This is because some certificates,
   such as those issued by the Gemological Institute of America, will not
   show the important measurements influencing cut (such as the pavilion
   angle and crown angle) and will not provide 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 judge the quality of a
   diamond cut, and the task is complicated by the fact that different
   standards are used in different countries (see proportions of the round
   brilliant).

   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 be complemented by a shallower crown angle, and vice versa.
   Graphs showing this trade-off are available from folds.net, by pressing
   Go on the HCA web service, and in Bruce Harding's article on Faceting
   Limits.

   Other proportions also affect the look of the diamond:
     * The table ratio is very significant.
     * The length of the lower girdle facets affects whether Hearts and
       arrows can be seen in the stone, under certain viewers.
     * Indexing the upper girdle facets
          + 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
            (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 girdle. These stones have less light leakage
            at the edge of the stone (for a given crown angle, pavilion
            angle, and table ratio), but does have a negative effect on
            the overall beauty of a diamond as shown in the GIA article
            Painting and Digging Out.
          + Solasfera is the only branded round modified brilliant diamond
            known to date that has no light leakage through out the stone
            and does not have any cheated or painted girdle, thus having
            more efficient and better optical performance.

   Several groups have developed diamond cut grading standards.
     * The AGA standards may be the strictest. David Atlas (who developed
       the AGA standards) has suggested that they are overly strict.
     * The HCA changed several times between 2001 and 2004. As of 2004, an
       HCA score below two represented an excellent cut. The HCA
       distinguishes between brilliant, Tolkowsky, and fiery cuts.
     * The AGS standards changed in 2005 to better match Tolkowsky's model
       and Octonus' ray tracing results. The 2005 AGS standards penalize
       stones with "cheated" girdles.

   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). The GIA announced in the fall of 2005
   that it will include a cut grade for round brilliant diamonds on every
   GIA Diamond Grading Report starting on January 1st, 2006. The single
   descriptive words are as follows: Excellent, Very Good, Good, Fair, and
   Poor.

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