In order to make a sparkling stone from a rough diamond, processing is necessary. This must be done very carefully because if mistakes are made the stone can disintegrate into many small fragments or can even burn up. The most important steps of the processing are cleaving or sawing, bruting and polishing. Because diamonds are composed of layers they can be split (cleaving). When faceting the diamond, one must take account of the “grain”, the direction in which the crystals have grown.

From rough to polished

To an important extent, the shape of the rough diamond determines what shape of diamond(s) can be polished from it. As a result of the sawing and polishing, the weight of the polished diamonds is considerably less than that of the rough stone, typically 60% less.

Cleaving

Cleaving (splitting) diamonds demands great knowledge on the part of the cleaver. The position where the stone is to be cloven or sawn is first marked with ink. Afterwards, the cleaver fixes the diamond to a cleaver’s stick with the aid of cleaver’s cement and, with another diamond, makes a V-shaped groove at the spot where the stone is to be cloven. He puts the blunt cleaving knife in the groove and gives a short blow with the mallet there. Then the diamond splits in two. The technique of cleaving is no longer practised very much. It has been largely replaced by sawing, or — with larger diamonds — by cutting with the aid of a laser beam.

Sawing

For sawing diamonds, a thin sawing disc (0.05 to 0.14 mm thick) made of phosphor bronze is used, the edge of which is coated with a mixture of diamond powder and oil. The stone is sawn at 4500 to 6500 revolutions per minute.

Cutting (bruting)

The still rough shape can be ground round by rubbing the diamond against another diamond — the “co-grinder”. The dust is collected and used for industrial purposes.

Polishing

Now the facets must be applied that make the diamond sparkle. In the past, this was done by securing the stone in a lead cap, which was held in place by a copper handle in wooden tongs. Precisely positioning the diamond in the cap was the work of the “setter”. Nowadays, the polisher places the stone directly in the polishing tongs. The facets are polished onto the stone using a horizontally rotating polishing wheel lubricated with oil and diamond powder. Through the polishing process, the stone sometimes loses as much as 70% of its weight.

Industrial applications

Since the industrial revolution, diamonds have found many applications thanks to their hardness. A selection of objects on the wall shows where that hardness counts.

• Drilling tools  To drill holes in hard stone, bits having drilling surfaces with diamond grit are used. (Collection: Brus.)

• Sawing blades  Saws with cutting edges coated in diamond grit can go through the hardest of stone. (Collection: Brus.)

• Surgical knives  Surgical scalpels often have a blade of optical grade CVD material. CVD (Chemical Vapor Deposition) is a method to produce synthetic diamond crystals by heating carbon-rich gasses to a very high temperature in a near vacuum. Layers of diamond crystals are applied on a template, such as the blade of this scalpel, “like frost growing on a window”. The gallery displays scalpels for cosmetic surgery, eye surgery, bypass surgery and general surgery. (Courtesy Element Six.)

• Dentist tools  Dentists use drills with a diamond drilling surface. (Collection: Brus.)

• Diamond plane  A plane whose cutting edge is reinforced with diamond, used to work extremely hard materials.

• Diamond window  In 1975 the Drukker Company of Amsterdam was commissioned by NASA to make a window for the Venus-Pioneer spaceship — one that would withstand the extreme temperature and pressure conditions in space. It also needed to be of great clarity to make observation possible. A round diamond of 3 mm thickness and 18 mm in diameter was polished from a 205-carat diamond from the South African Premier mine; 10 additional small windows each 9 mm in diameter were mounted around it.

• Rough diamond  A rough diamond in a colour unsuitable for use in jewellery is crushed for industrial use.

• Lab grown diamond  Since the nineteen-fifties it has been possible to produce diamond artificially. Today 95 to 99% of the diamond used in industry is synthetic — and the same growth process underlies lab-grown jewellery diamonds.

Showpieces in this gallery

• Golden Racket of the Diamond Games of Antwerp  The tournament earned its nickname “Golden Racquet” because if a player won three times within a five-year span, she would receive a special trophy: a life-size, 13.2-pound gold racquet studded with 1,420 diamonds and valued at one million dollars. Only one player has achieved this in the history of the Diamond Games — Amélie Mauresmo took the piece of art home in 2007.

• Katana, Japanese Sword  Katana is the Japanese word for sword. This masterpiece was fabricated in the famous glass workshops of Murano, Venice; the solid piece of glass was molded into its final shape by hand at a temperature of 1200 degrees Celsius — an extremely delicate process known only to the Murano glass experts. Monique Zegerius, a Dutch glass artist, designed this Katana and commissioned the sword to be made in Murano to her specifications. Lili B., a Dutch jewel designer, had the difficult task of setting the diamonds and rubies. Drilling into this glass is impossible, because it would shatter; a very special process of high-pressure water “drilling” was used to attach the gold to the glass. The sword carries 1967 diamonds (54.48 carats total) and 494 rubies (10.69 carats total), set in 18-carat white and yellow gold.

• Tiara from the Russian Imperial Treasury (replica)  The last empress of Russia to wear this 19th-century tiara was Alexandra Feodorovna, wife of Tsar Nicholas II. After the end of the monarchy and the murder of the imperial family, a large portion of the Russian crown jewels — this tiara included — was sold off by the communist regime. A small part of the originally enormous collection is currently on public display at the Kremlin Museum.

• The Imperial State Crown of England (replica)  For the coronation of Queen Victoria in 1838, her predecessor’s coronation crown was not used; a new crown was forged for her. Since then this has been known as the Imperial State Crown and is usually worn by the English head of state every year during the ceremonial opening of Parliament. For the coronation of George VI in 1937, the crown frame — by then nearly a century old — proved too fragile. All the precious stones, including the Cullinan II diamond, the large red spinel also known as the “Black Prince’s Ruby” and the sapphire from Edward the Confessor’s coronation ring, were precisely reset into a new crown of exactly the same shape and design.

• Sceptre of Charles II of England  Part of the English coronation regalia since 1661, the sovereign’s sceptre of King Charles II is set with 393 gemstones. During the coronation ceremony the reigning king or queen holds this sceptre in the right hand, while the sceptre with the dove is clasped in the left. Since 1910, the largest of the Cullinan diamonds — the “Star of Africa” (530 carats) — has glittered at the top of the sceptre.

• Circlet of Mary d’Este, Princess of Modena  Queen Mary d’Este first wore this circlet, or diadem, at her coronation in 1685, during the procession from the palace to the church. That became a custom which continued until 1831. On the way back she wore the state crown.

• Crown of the Queen of Bavaria  In 1806 Bavaria acquired the status of kingdom; two crowns, a sceptre, an orb and a sword were ordered from the Parisian jeweller Biennais. The crown made for the queen, set with pearls, diamonds, rubies and emeralds, is small in size — being 11 cm in diameter — and, as was customary for many queens in the 19th century, it balances on top of the head.

• Crown of Louis XV of France  The crown worn by Louis XV at his coronation in 1722 is famous because two magnificent diamonds were set in it: the Regent was positioned in the central fleur-de-lis ornament directly above the headband, while the Sancy was placed in the topmost leaf of the fleur-de-lis adorning the crossed arches. Today the original crown is displayed in the Louvre in Paris, set however with “diamonds” of glass.

• Laurel wreath of Emperor Napoleon I of France  For his coronation as “Emperor of the French by the Grace of God and the constitution of the Republic” on 2 December 1804, Napoleon I took the Roman emperors as his example. He crowned himself with a golden laurel wreath.

• Crown of Queen Elizabeth, the Queen Mother  Made for her coronation in 1937. The most important stone is the 105-carat Koh-i-Noor in the middle of the front cross. The Koh-i-Noor was re-polished by two master polishers of Coster Diamonds from Amsterdam in 1852.

• Collier of the Maharaja of Baroda  In 1853, a female slave in the Brazilian Bagagem mine discovered a large diamond of more than 254 carats. As a reward she received her freedom and an annuity from the mine owner. The stone was cut at the Coster Company in 1854 by the well-known cutter Louis Voorzanger. After the Star of the South (128.8 carats) had been displayed at the Paris World Exhibition of 1855, it was only sold ten years later, to the ruler of the Indian state of Baroda. The diamond was the centrepiece of the state necklace of this royal house, together with two other famous diamonds, the English Dresden and the Empress Eugénie. In 2004 the stone was purchased by Cartier, the Parisian jewellers’ house.

• Cullinan I through IX  All nine Cullinan stones cut from the original rough diamond are part of the British Crown Jewels.

• The rough Cullinan, 3,106 carats  Found in 1905 in the Premier Mine, South Africa. The firm of Asscher in Amsterdam was commissioned in 1908 to cleave and polish the stone.

• Original lead holder for polishing of the Cullinan  The stone was set in a lead cap during polishing; the cap was held by a copper handle in the polishing tongs.

• The Koh-i-Noor, original and present state  In 1852 the diamond was re-cut by the famous cutter Louis Voorzanger and bruter Fedder of Coster Diamonds, on the orders of Queen Victoria. The stone was given an oval brilliant form and reduced in weight from 186 to 105.60 carats. In 1937 the Koh-i-Noor was set in the coronation crown of Elizabeth, the Queen Mother.