DIAMOND CUTTING

Rough diamonds are not brilliant and can appear greasy. Diamond cutting encompasses a number of processes that bring out the beauty of gem diamonds. These processes include cleaving, sawing or laser cutting, and polishing. A diamond cutter seeks to enhance the brilliance and fire of each stone and to eliminate imperfections, such as cracks and cloudiness. The cutter develops a plan that will accomplish these goals while still producing a gem of the greatest size and hence maximum value. About half of a natural diamond’s size is lost in diamond cutting.

Examining the stone is the first step in diamond cutting. The cutter determines where cleavage planes lie and decides how the stone can best be divided by cleaving and sawing. Ink marks on the rough diamond serve as a guide for the shaping to follow.

The cutter next places the diamond firmly in a holder for cleaving. A light blow of a hammer on the cleaving iron, which is held against the diamond parallel to the cleavage plane, cleaves the stone. In present-day practice cutters more often saw diamonds or cut them with a laser rather than cleave them. The saw is a thin metal disk, the edge of which is impregnated with a mixture of diamond dust and oil.

Polishing, the final step in the cutting of a diamond, consists of forming the facets of the finished stone. Cutters most often choose the “brilliant” form, which has 58 facets. During the polishing process a mount called a dop firmly holds the gem. A flat, horizontally revolving cast-iron wheel coated with a mixture of diamond dust and oil forms the facets. The cutter holds the stone in its dop against the surface of the wheel until the facet forms. In the course of polishing, the cutter moves the stone many times in its dop to present new surfaces for polishing.

USE DIAMOND IN JEWELRY

Jewelry of later periods falls into two main groups: diamond jewelry, which was usually conservative in design, and jewelry that reflected changing fashions in clothes and the arts. With the introduction in the 17th century of new methods of faceting gems to give them greater brilliance, the diamond became the preferred stone for precious jewelry, a reference that remains. At the same time, in the 18th and 19th centuries, industrial development brought mass production of more popular jewelry in cheaper materials. In addition to diamond tiaras, rings, and brooches of naturalistic design, there was less costly jewelry in the neoclassical style inspired by originals excavated at Pompeii, and in revivals of Gothic, Renaissance, and Egyptian styles. The materials utilized, in addition to gold and semiprecious stones, included base-metal alloys, paste (for imitation gemstones), steel, and cast iron. Techniques included mechanical processes for stamping and cutting out patterns and settings.

In the case of both luxury jewelry and popular jewelry, a characteristic arrangement was a matched set, or parure. A woman's parure often included a tiara or ring in addition to the basic combination of necklace, earrings, and brooch. A man's parure, in the 18th century, consisted of buttons, shoe buckles, sword hilt, and the insignia of knightly orders. Many magnificent parures and other jewels were created for the royal houses of Europe, which for several hundred years have accumulated permanent collections of coronation regalia, state and personal jewelry, and important single stones like the Koh-i-noor and Hope diamonds. Many of the brilliant crowns have been reset, broken up, or lost, but a variety of impressive collections remain in the Tower of London, the Vienna Treasury, and the Kremlin. Jeweled accessories were also fashionable. These included watchcases, snuffboxes, seals, and thimble cases.

The jewelry worn in colonial America was mostly imported from Europe. Although records exist of simple jewels made in the colonies at the time, almost none has survived.

The most opulent jewelry was made during the Second Empire in France, when a demand for costly gems set the style for the lavish use of diamonds and pearls. With the emphasis on extravagant display and the intrinsic appeal of precious stones, the workmanship of the metal settings was neglected and became inferior. Only at the end of the 19th century did Peter Carl Fabergé reintroduce exacting craftsmanship in jewelry and in such accessories as boxes, cane handles, fans, and picture frames. Like the goldsmith-jewelers of the Renaissance, Fabergé specialized in the contrast of colors and materials, and his most original designs are those that combine gold, enamel, and various gems

HISTORY OF DIAMOND

Diamond, mineral form of the element carbon, valued as a precious stone. Diamond is the hardest natural mineral and has many other exceptional properties that collectively make it an important industrial and scientific material. Unique geologically, diamonds form at great depths within Earth and are typically billions of years old.

Diamond is the hardest known natural material (third-hardest known material after aggregated diamond nanorods and ultrahard fullerite), whose hardness and high dispersion of light make it useful for industrial applications and jewelery. Diamonds are specifically renowned as a material with superlative physical qualities — they make excellent abrasives because they can be scratched only by other diamonds, Borazon, ultrahard fullerite, or aggregated diamond nanorods, which also means they hold a polish extremely well and retain luster. About 130 million carats (26,000 kg) are mined annually, with a total value of nearly USD $9 billion.About 100,000 kg are synthesized annually.

The name “diamond” derives from the ancient Greek adamas (αδάμας; “invincible”). They have been treasured as gemstones since their use as religious icons in India at least 2,500 years ago— and usage in drill bits and engraving tools also dates to early human history.

Popularity of diamonds has risen since the 19th century because of increased supply, improved cutting and polishing techniques, growth in the world economy, and innovative and successful advertising campaigns. They are commonly judged by the “four Cs”: carat, clarity, color, and cut.

Roughly 49% of diamonds originate from central and southern Africa, although significant sources of the mineral have been discovered in Canada, India, Russia, Brazil, and Australia. They are mined from kimberlite and lamproite volcanic pipes, which brought to the surface the diamond crystals from deep in the Earth where the high pressure and temperature enables the formation of the crystals. The mining and distribution of natural diamonds are subjects of frequent controversy such as with concerns over the sale of conflict diamonds by African paramilitary groups. There are also allegations that the De Beers Group misuses its dominance in the industry to control supply and manipulate price via monopolistic practices, although in recent years the company's market share has dropped to below 50%.

Diamonds are crystals composed of pure carbon. In nature, diamond crystallizes from hot carbon-rich fluids. This crystallization requires tremendous heat and pressure—1000 to 1200°C (1800 to 2200°F) of heat and 50 kilobars of pressure. (One bar is based on the pressure the atmosphere exerts at sea level, about 1.02 kg per sq cm, or 14.7 lb per sq in; 50 kilobars is 50,000 bars.) The pressures and temperatures at which natural diamond forms only occur deep underground. Scientists believe that diamonds form at depths greater than 150 km (93 mi), and there is evidence that some diamonds formed as deep as 670 km (420 mi) beneath Earth’s surface.

Concentrations of diamonds great enough to be economically feasible for mining are usually found in Earth’s oldest continental regions, called cratons. Cratons form the cores of most continents and consist of inactive geological areas more than 2 billion years old with thick crust and deep roots extending into the mantle beneath. Craton conditions are ideal for diamond formation and preservation. Scientists have determined the ages of some diamonds by dating mineral impurities trapped within the diamonds. These data reveal that most cratonic diamonds are ancient, some older than 3 billion years.

Much younger volcanic rocks—kimberlites and lamproites—pass through the cratonic rocks in a liquid form called magma during their rapid ascent to Earth’s surface. These flowing veins of rock act as carriers of diamonds and other rock fragments. After eruption they solidify, forming funnel-shaped kimberlite “pipes.” These pipes are primary diamond deposits. Many diamonds are recovered at a distance from their primary deposits in secondary alluvial deposits, which are loose eroded materials left behind by flowing water. In some instances diamonds are also found in sandstones, conglomerates, and other sedimentary rocks that presumably solidified from former alluvial deposits. Wind and glaciers can also transport diamonds from their point of origin at Earth’s surface.

Small, generally low quality diamonds form in rocks at shallower depths under pressure conditions that are higher than usual for those depths. Tectonic movement, rather than magma, transports these diamonds to Earth’s surface. Deposits of this type occur in areas such as Kazakhstan and typically involve the collision of a continental and an oceanic plate followed by rapid uplift of deeply buried rocks. Diamond deposits brought to the surface by tectonic movement are generally younger than kimberlitic diamonds, and typically consist of microdiamonds (less than 1 mm across) or graphite relics of larger diamonds.

Diamonds are also found in meteorites and near meteorite craters on Earth’s surface. Extremely small diamonds (nanodiamonds) occur in many types of meteorites and have a lower density than other diamonds. Meteorites can also produce pressure and heat at the moment of impact sufficient to transform carbon into diamond. Diamond found in a type of meteorite called ureilite is thought to form directly from graphite contained in the meteorites upon impact. Impact-crater diamonds are opaque and range from very small to around a centimeter in diameter.