Until the 14th century, diamonds were not cut at all. They were worn in their natural octahedral crystal form, the same flat-sided, double-pyramid shape that emerges when octahedral rough is simply polished on a grinding wheel. The point cut produced a geometric shape with no brilliance in the modern sense: a pointed top, a pointed bottom, eight triangular faces. The brilliance of a well-cut modern diamond, the fireworks of light return that makes it extraordinary, was simply not achievable with the grinding tools and optical understanding available before the 15th century. It took five centuries of progressive technical improvement to get from the point cut to the Tolkowsky brilliant. : Ogden, J. (1982), Jewellery of the Ancient World, Trefoil Books, London; Tolkowsky, M. (1919), Diamond Design, E&FN Spon, London

The point cut and table cut (14th–15th centuries)

The point cut, polishing the natural faces of octahedral rough, was the earliest form of diamond cutting. It produced a geometric, transparent stone but with minimal brilliance. The table cut, developed in the 15th century, removed the top point of the octahedron to create a flat table facet, with a similar culet facet at the bottom. The table cut produced somewhat better light return but was still far from the optical performance of later cuts (Ogden, 1982, op. cit.; historical documentation of early cutting development).

The rose cut (16th–17th centuries)

The rose cut emerged in the 16th century and was widely used through the 17th and 18th centuries. A rose-cut diamond has a flat base and a domed top covered with triangular facets, typically six, twelve, or twenty-four facets depending on the style. The rose cut made better use of flat rough crystal than the table cut, which required a more equidimensional stone. The Sancy Diamond (55.23ct, now at the Louvre) is a famous example of an unusual double rose cut (historical documentation of rose cut development; Balfour, 1987, Famous Diamonds).

The old mine cut and old European cut (17th–19th centuries)

The old mine cut, a cushion-shaped stone with a high crown, small table, large culet, and hand-cut facets, was the dominant cutting style of the 17th through 19th centuries. It represents the cutting technology of the era: facets were shaped by eye and hand on a spinning grinding wheel, resulting in characteristic irregular facet shapes and slightly off-round girdles. The old European cut (late 19th–early 20th century) refined this into a more circular shape with more consistent facets as mechanical precision improved. Both styles produce a distinctive light return pattern, warmer, more diffuse than a modern brilliant, that is now valued for its antique character (Ogden, 1982; historical cutting documentation).

Tolkowsky's ideal brilliant (1919)

In 1919, Marcel Tolkowsky, a young diamond cutter from an Antwerp cutting family, studying for a mathematics degree at the University of London, published Diamond Design: A Study of the Reflection and Refraction of Light in a Diamond. Using geometric optics and mathematical analysis of light behaviour in a transparent crystal of known refractive index, Tolkowsky derived the proportion parameters that maximise brilliance and fire simultaneously: crown angle 34.5°, pavilion angle 40.75°, table 53%, and a specific relationship between crown height, pavilion depth, and girdle diameter (Tolkowsky, M., 1919, Diamond Design, E&FN Spon, London).

Tolkowsky's proportions became the foundation of the modern round brilliant cut and, eventually, the GIA Excellent cut grade system. His mathematical derivation, setting out, for the first time, the exact geometry that maximises the optical performance of a cut diamond, is still referenced in every serious discussion of diamond cut quality (Reinitz et al., 2006, op. cit.; GIA cut grade system documentation).

Primary sources

GIA Diamond Grading documentation. gia.edu/diamond-grading. Gemological Institute of America. [Cut grade system; proportion parameters; polishing and symmetry assessment; planning methodology context.]

GJEPC (Gem and Jewellery Export Promotion Council). gjepc.org, Mumbai. [India cutting industry data; Surat manufacturing statistics; export figures.]

Reinitz, I. et al. (2006). "Development of the GIA Diamond Cut Grading System." Gems & Gemology, 42(3), GIA. [Cut grade system basis; proportion parameters and their effect on light performance.]

Sarine Technologies product documentation. sarine.com. [Galaxy family scanning instruments; planning software; mapping of inclusions and proportions for yield optimisation.]