The cut of a stone brings out and exposes the natural beauty of the stone.
The need to accessorize is older than human written history. Our Stone Age ancestors learned to shape rocks as tools and weapons before they could even grow tomatoes. If it was a colored rock, they might use it as a religious object or as personal ornament. Carving, engraving, and perforating are most probably the oldest techniques for shaping stones.
In China , ceremonial jade objects carved in simple designs were buried with the dead before 3000 BCE. By the Zhou Dynasty (112 to 256 BCE), lapidaries were carving nephrite jade, chalcedony, and serpentine into functional, decorative, and ceremonial objects. With few interruptions, gem carving has remained an important part of Chinese art ever since.
Around 3000 BCE, Mesopotamian stone cutters were using primitive lapidary wheels to shape and polish stones. They had no hard abrasives, but most gems available to them – turquoise, chalcedony, and lapis lazuli – were soft enough to be fashioned with sand.
Gems, one of the first global commodities, were carried around the world as the Roman Empire expanded to the East. Exquisite gems like ruby, sapphire and diamond were introduced to the Old World . Along with these fine gems came an even more important substance – the emery, or granulated corundum (Mohs hardness 9). The emery was, to the European gem-cutter, as important as diamond powder to the weapon industry during the Second World War. They could work much faster and could handle harder materials.
Diamond cutting techniques probably originated from India . In ancient times, this was limited to chipping or grinding. In ancient India gemstones were valued for their magical and astrological properties. It was thought thay modifying the natural state of a gem in any way would ruin the magical properties and render it useless. At most, the cleaving techniques of diamond were used to get flat faces on diamonds. The European travelers who visited India for its treasures imported diamonds from the Golconda mines near Hyderabad to Europe for cutting. They were ultimately transported back to India, and made a part of the Kings, Moguls and Maharaja’s treasuries.
The earliest European diamond-cutting industry is believed to have arisen in Venice , a prominent trade capital, starting sometime after 1330. Indian precious stones reached Venice by two Mediterranean routes – the southern route, by way of Aden , Ethiopia , and Egypt , and the northern route through Arabia , Persia , Armenia , and Turkey . When the Portuguese discovered a direct sea-route to India , Antwerp flourished as a diamond center because the city was well situated to receive vast supplies of rough from Lisbon as well as from Venice . The East Indian gems, many of which are doubtless very ancient, were polished in the usual oriental fashion by merely rounding off the angles. Among church jewels in Europe are a few diamonds of unknown age and source, cut four-sided, with a table above and a pyramid below. Several cut diamonds are recorded among the treasures of Louis of Anjou in the third quarter of the 14th century. The modern method of brilliant cutting, however, is attributed to Lodewijk van Berquem, of Bruges , a city that was situated on the gem trade route (Check the diamond museum in Bruges , http://www.diamondhouse.net ).
In I475, Van Berquem cut several celebrated diamonds sent to him by Charles the Bold, Duke of Burgundy. Van Berquem’s apprentices later settled in Antwerp and Amsterdam , chief centers of diamond cutting ever since. Peruzzi, an Italian architect and painter of the Roman school, worked out the theory of the well-proportioned brilliant of 58 facets. Some very fine work was done early in London also, but most of the cutters were Jews, who, being persecuted in England , finally moved to Amsterdam and Antwerp .
The scientific breakthrough: the Ideal Cut. European cut was more evident in the late eighteenth century till the early twentieth century. Many experiments were done on the old European cut during the early twentieth century, with regards to facet positioning and angles. Most notable was an experiment done by Henry Morse and Marcel Tolkowsky. In1919, Mr.Tolkowsky confirmed the two-dimensional parameters for ideal proportions for modern round brilliant diamonds. (Check the text in http://www.folds.net/diamond_design/index.html.) In1930 , Lazare Kaplan (a first cousin to M. Tolkowsky) began cutting diamonds according to Tolkowsky ‘s ideal proportions. The grandson of Marcel , Gabi Tolkowsky , is one of the most accomplished cutters in the world .
With the advance of modern optics it was possible to define the I deal cut in terms of structure and the facets relative angles and proportions, for any type of gemstone . Since the purpose of cutting a gemstone is to maximize its beauty, transparent gemstones are faceted to enhance interaction with light. This light interaction enhancement is through reflection, refraction, and selective absorption. In a well cut, clean stone, we can observe the following optical phenomena:
Brilliance: The amount of light returned to the eye, or brilliance, depends on how well the stone reflects and refracts light. This includes dispersed wavelengths, which are reflected from the internal surfaces and returned to the eye. Dispersion: The occasional flash of color, or fire, particularly when viewing a gem in strong, direct light. In optical terms, dispersion is the separation of white light into spectral colors, each of which vibrates at a different frequency. Dispersion flashes may be seen in any color.
Scintillation: This refers to the flashes of light, or the sparkle, you see when a gem is moved in the light. Scintillation is best when clarity is high. Luster: Luster is the perceived reflection and surface appearance of a polished gem. Generally, the higher the refractive index of the gem, the higher its luster. For example, pearls and amber have lower luster and refractive indexes than diamonds and rubies.
Extinction : Extinction describes dark areas where little or no light returns to the eye. This happens when light waves interpolate. Obviously, this phenomenon is undesirable.
In the real world , the Ideal cut in most cases is impossible, because of the prohibitive weight loss. Usually, cutting is like politics – an artful combination of compromise, hiding faults, and, in the case of gemstones, retaining weight. When we evaluate the quality of the work done, the important characteristics to take into account are proportion and symmetry.
Depth percentage : is the ratio between the depth of the stone (the distance from the culet to the table) and average diameter of the girdle. Depending on the gem critical angle, the percentage should be an average of 70%. Deep stones are usually lacking brilliance, while shallow stones tend to show a “fish eye” and not enough reflection.
Girdle outline : the girdle should be well polished, even all around, and neither too thick nor too thin.
Culet position : the culet should be well centered, otherwise light reflection will be asymmetric.
Table facet : the table should be well centered and, not tilted; this is, it should be parallel to the girdle plane.
Facets junctions : facets should meet nicely, all together in a sharp point, and not overlapping.
Polish : no visible wheel marks or scratches.
Cutting styles : The terms refers to the way the cutter lays out the facets on a stone. There are few factors influencing the cutting style, and in precious stones the important factor is the retention of weight. In less precious stones, brilliance may come first. Any gemstone has two main parts, the crown, and the pavilion (culet). The pavilion is where the weight is mostly retained; so a step cut is usually applied in the case of precious stones. It enables the cutter to follow the rough shape of the stone. The crown usually is cut in brilliant or star cut. The mixed cut (brilliant crown/step pavilion) is the market standard for precious stones.
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The Gemcal team