Diamond cutting

Diamond cutting is the highly specialised practice of transforming a rough diamond into a polished, faceted gemstone. Owing to the exceptional hardness of diamond—ranking highest on the Mohs scale—its shaping requires advanced tools, precise techniques and considerable expertise. The first guild of professional diamond cutters, known as the Diamantaire, emerged in Nuremberg in 1375 and laid the foundations for the development of refined cutting styles. Diamond cutting encompasses two meanings: the overall shape of the gem, such as round, oval or square, and the quality of the cut, which determines brilliance, symmetry and market value.

Historical Background and Global Centres

The earliest noteworthy innovation in diamond cutting was the Point Cut of the late fourteenth century, a technique that shaped the gem according to the natural geometry of an octahedral crystal. Over time, more sophisticated cuts evolved, enhancing both the optical qualities and market desirability of diamonds.
Diamond processing is highly concentrated in a few global centres. Major trading hubs include Antwerp, Tel Aviv and Dubai. Rough diamonds are primarily sent to cutting and polishing centres in India and China, with cities such as Surat, Guangzhou and Shenzhen holding the vast majority of global market share. A smaller but historically important role is played by New York City and Amsterdam.

The Diamond Cutting Process

The full cutting procedure consists of several interrelated stages. Although precise methods vary depending on the stone’s characteristics, most manufacturing follows a broadly similar workflow.
PlanningModern planning relies heavily on advanced software and three-dimensional scanning technologies. Manufacturers create digital models of the rough stone and photograph internal inclusions, integrating this information to determine optimal cutting strategies. The planning stage aims to maximise both the financial return from the rough stone and the speed at which the finished diamond can be sold. Important considerations include rough shape, internal flaws, weight retention and expected market demand.
Cleaving or SawingCleaving involves splitting a diamond along one of its natural cleavage planes. A groove is cut using lasers or another diamond, and the stone is then split with a precision strike from a steel blade. Sawing, in contrast, employs diamond-coated saws or lasers to cut through the stone irrespective of cleavage planes. Both techniques determine the initial division of the rough into workable sections.
BrutingBruting shapes the girdle—the outer edge—of the diamond. Traditional bruting is performed by grinding two diamonds against each other, though modern factories also use diamond-impregnated discs or laser technology. Software now measures roundness to within a tenth of a millimetre for an excellent-cut stone.
PolishingPolishing completes the diamond’s facets and produces its optical qualities. A crossworker blocks the main facets, ensuring correct angles and weight preservation. A brillianteer then adds the smaller facets—such as the star, upper girdle and lower girdle facets—thereby refining symmetry and brilliance.
Final InspectionThe finished diamond undergoes rigorous quality control, including acid cleaning and examination for symmetry, polish and overall cut grade.

Planning Considerations and Optimisation

Achieving maximum value from a rough diamond is a key objective. The practice is influenced by both economic and physical considerations and represents a balance between artistry and engineering.
Weight RetentionDiamond prices increase sharply at key carat thresholds, making weight retention an essential consideration. A single rough diamond may be cut into two stones if that yields a higher combined value. Rough octahedra often produce two round or square brilliant stones, while irregular crystals such as macles are typically cut into fancy shapes to reduce waste. Despite modern techniques, up to half of the original rough weight is generally lost in cutting.
Colour RetentionThe cutting style can significantly affect the colour grade of coloured diamonds. Shapes such as the radiant cut are employed to intensify colour saturation. Natural green diamonds, whose colour often resides near the surface due to irradiation, are cut with portions of the rough surface left intact to preserve their distinctive hue.
Turnaround MinimisationManufacturers may prioritise rapid marketability over maximum theoretical yield. A cut that produces stones likely to sell quickly may be chosen even if it results in lower overall value. Such decisions depend on inventory needs, client preferences and market trends.

Recutting and Market Trends

Diamond styles fluctuate with consumer demand, prompting jewellers to recut older stones into more desirable shapes. The marquise cut, popular in the late twentieth century, has often been reshaped into ovals or pears to enhance resale value, generally involving a modest loss of weight. Historical recutting—particularly in the eighteenth century—also reflects aesthetic trends, with Indian diamonds frequently altered to meet European tastes.

Significance of Material Properties

Diamond cutting is possible only through the distinctive physical properties of the gem. Although diamond is the hardest known natural material, its hardness varies according to crystallographic direction, allowing experts to grind and shape it using diamond-coated tools. This anisotropy is central to cleaving, bruting and facet placement and underlies both the challenges and the precision associated with diamond cutting.

Artistic and Economic Importance

The transformation of a rough diamond into a brilliant gemstone merges technical skill with aesthetic judgement. Each decision—from initial planning to final inspection—affects the diamond’s brilliance, value and market appeal. As the global trade continues to evolve, diamond cutting remains an essential industry that combines centuries-old craftsmanship with sophisticated technology, ensuring that each stone achieves its full potential as a polished gem.