One of the hardest substances on earth, only a diamond is hard enough to cut other diamonds. Polishing and mounting add brilliance to the stone and increase it's value. Diamond cutting can be traced back to the late Middle Ages. Prior to this time, diamonds were used in their natural octahedral state.
The first improvements on nature's design involved a polishing of the crystal faces, which was called the "Point Cut". As further refinement progressed, one half of the crystal would be cut off, creating the "Table Cut". At the time, diamonds were valued primarily for their luster and hardness. Table Cut diamonds appeared black to the eye. The Modern Round Brilliant cut (below) is the culmination of several hundred years of experimentation and development.
Cutting a raw diamond into a faceted and polished gem-quality stone is a multi-step process. Each step is critical to the final outcome. The steps are:
- Marking
- Cleaving
- Sawing
- Bruting (Girdling)
- Faceting
Marking: A rough stone is marked prior to cleaving or sawing to determine the direction of the grain or "cleavage", eliminate waste, and bypass inclusions or imperfections. The natural shape of the rough stone will also be a major factor in deciding how to cut the stone. An octahedron can be cut into one or two Round Brilliants but a square Princess cut will result in the least amount of waste due to the square shape of the stone. Asymmetrical crystals such as macles are used primarily for fancy cuts. Cubic shapes are ideal for a square Princess or Radiant cut. High-tech computerized helium and oxygen analyzers are now used to evaluate a stone prior to cutting.
Cleaving: Cleaving refers to splitting a stone along its grain by striking it. A rough stone is cleaved if there are conspicuous defects and/or inclusions which would prevent it from being made into a single gemstone. Cleavage is the tendency of crystalline materials to split along definite planes. Due to its atomic structure, a diamond can be cleaved in four directions parallel to each of the four octahedron crystal faces. Cleaving is a critical step as a mistake by the "cleaver" could shatter the stone.
Sawing: A stone-cutting saw is a thin disk made of phosphor bronze. As the saw blade rotates it continues to pickup or "recharge" itself with diamond dust which is the cutting agent. It can take several hours for the saw blade to cut through a 1k rough diamond.
Bruting: The rough is placed in a chuck on a lathe. While the rough stone rotates on the diamond lathe, a second diamond mounted on a dop is pressed against it, rounding the rough diamond into a conical shape. This step is also referred to as rounding or bruting.
Faceting: To facet a "Round Brilliant", a "blocker" or "lapper" will cut the first 18 main facets, then a "brillianteer" will cut and polish the remaining 40 facets. The cutting (placing) and polishing of each facet is accomplished by attaching the stone to a dop stick and pressing it against a revolving cast iron disk, scaife, or lap on a Facetron that has been charged with diamond dust. During this faceting stage the angles of each facet must be cut to an exacting standard in order to yield maximum brilliancy and maintain symmetry.
