A great deal of planning, patience, wisdom and experience goes into transforming the world's hardest material into the beautiful diamonds. Diamond cutting is the art, skill and, increasingly, science of changing a diamond from a rough stone into a faceted gem. Diamond cutting requires specialized knowledge, tools, equipment, and techniques because of its extreme hardness.
Diamond manufacturers analyze diamond rough from an economic perspective, with two objectives guiding decisions about how a faceted diamond will be cut. The first objective is that of maximum return on investment for the piece of diamond rough. The second is how quickly the finished diamond can be sold.
There are many details that must be considered when planning to cut the diamond, such as, size, shape, cleavage planes and inclusions. The goal of the diamond cutter is to have the most carat weight possible at the lowest production cost, while having the best cut. Scanning devices are used to get 3-dimensional computer models of the rough stone. Also, inclusions are photographed and placed on the 3D model, which is then used to find an optimal way to cut the stone. If the diamond is incorrectly marked by even a fraction of a millimeter, the result can be a difference of thousands of dollars! Another risk is cleaving the diamond in an improper position, resulting in the diamond shattering and becoming worthless.
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.
A stone-cutting saw is a thin disk made of phosphor bronze. As the saw blade rotates it continues to pick up or "recharge" itself with diamond dust which is the cutting agent. It can take several hours for the saw blade to cut through a 1ct rough diamond.
Bruting is the process whereby two diamonds are set onto spinning axles turning in opposite directions, which are then set to grind against each other to shape each diamond into a round shape. This can also be known as girdling. The bruting process is only necessary for round brilliant diamonds; fancy cut stones need a different preparation.
Polishing is the name given to a process whereby the facets are cut onto the diamond and final polishing is performed. The process involves the steps of blocking, faceting, and polishing.
There are two phases of the polishing process, the first is blocking. The blocking stage sets the standard for how much brilliance the diamond will have because it establishes the basic symmetry of the stone. Blocking creates the first 17 or 18 facets of the diamond. When dealing with a small diamond, the polishing process stops here. Larger diamonds continue on to the second phase, called brillianteering.
A brillianteer is a diamond polishing specialist who polishes the final facets of the stone. This is the stage that ultimately determines the fire and brilliance. The brillianteer cuts an extra 40 facets onto the stone to create the round brilliant cut diamond. Even minor inconsistencies in symmetry and proportions have the potential to make a difference between a diamond full of sparkle and life or diamond one that is dull.
The final stage involves thoroughly cleaning the diamond in acids, and examining the diamond to see whether the stone meets the quality standards of the manufacturer. At this point, the diamond wholesaler or jeweler may choose to have the stone analyzed by a reliable independent lab to receive a diamond grading report or may choose to sell the stone without a certification.