Selling Diamonds

(via Diamond Promotion Service) Diamond Cutting: 28. The beauty of a gem diamond depends on the way it handles light. Diamond cutting unlocks this beauty.

The ancient Indian lapidaries learned that the surfaces of a diamond could be polished by rubbing another diamond against them. This enabled the diamond to reflect more light, and in ancient times the diamond was called the Venus stone because of its brightness. In the 15th century important discoveries were made which resulted in even brighter stones through the grinding of additional facets or planes. More than two centuries later a Venetian cutter named Peruzzi invented the 58-facet form for round diamonds that is basic to today’s cutting. In 1919 Marcel Tolkowsky, a physicist, developed the relationship of facet angles that is considered ideal for modern cutting.

Antwerp and Israel are the largest diamond cutting centers in the world. Other important centers are Amsterdam, United States, India, West Germany and South Africa. Cutting is also done on a lesser scale in England, Puerto Rico, Russia, France and Portugal. Each center has gradually, over the years, come to specialize in cutting a particular quality of diamonds. Cleavages and chips are, in the main, worked in Antwerp; stones and shapes in the United States; and melee in Amsterdam, Israel and West Germany.

29. Marking. The first step in diamond cutting is an examination of the rough stone by the planner, usually a master cutter. Using his loupe, or magnifying glass, he studies every aspect of the stone. For very large diamonds, this study can go on for months, but for the average diamond the study is done in a few minutes. Nevertheless, every diamond must be studied, no matter how small it is.

The planner has to be conscious of two factors. Under normal circumstances, a rough diamond loses more than half its weight in the cutting process; so the planner has to determine the finished shape that will retain as much weight as possible. Most diamonds contain natural imperfections, or inclusions; so that planner has to position the finished shape and direct the cutting so that as many inclusions as possible can be ground away and the remaining inclusions will offer minimum interference with the passage of light through the stone. Sometimes, to eliminate a major inclusion, the planner will have a stone cut smaller than it could be.

Then he marks the diamond with India ink to indicate how the cutting will go. The principal mark shows how the stone must be divided. An octahedron crystal is usually divided just above the middle, and both parts are cut into round diamonds. An irregular piece of rough may be divided into several pieces, and each piece will be cut into a finished gem. When a piece of rough is already close to the shape of a finished gem, it may not be divided at all but just ground down into the finished shape.

30. Sawing. Most octahdedron crystals, and many irregular shapes, are divided ‘against the grain’, and so they are sawed. Only diamond will cut diamond; therefore, the saw is a thin disk of phosphor bronze, its edge coated with a paste of oil and diamond dust. The saw is mounted vertically and spins at high speed. The diamond is set into a clamp so that it can be lowered against the saw’s edge in the plane along which it must be divided. Gravity keeps the stone against the saw while it is being cut.

It takes hours to cut through even a small diamond. However, one sawyer can handle a batter of saws, checking each stone at intervals to ensure that is being sawed correctly. The deviation of even a hair can affect the finished gem.

Selling Diamonds (continued)