Gabriel "Gabi" Tolkowsky (born 1939, Antwerp) stands among the most celebrated diamond cutters of the twentieth century — and, by most accounts, of any century. A fifth-generation member of the Tolkowsky dynasty, a family whose name is inseparable from the scientific and artistic development of the modern brilliant cut, Gabi Tolkowsky brought to his work an inheritance that was simultaneously mathematical, optical, and deeply personal. He is best known internationally for two achievements that remain without parallel in the history of gem cutting: the fashioning of the 273.85-carat Centenary Diamond, the largest known diamond to carry a D colour grade and an internally flawless clarity grade from the Gemological Institute of America, and the cutting of the 545.67-carat Golden Jubilee, the largest faceted diamond in the world. Together, these two stones represent the outer boundary of what human hands, guided by extraordinary intellect, have achieved with rough diamond.

The Tolkowsky Dynasty

To understand Gabi Tolkowsky, one must first understand the family tradition from which he emerged. The Tolkowsky name entered gemmological history decisively in 1919, when his great-uncle Marcel Tolkowsky published Diamond Design: A Study of the Reflection and Refraction of Light in a Diamond, a monograph that applied mathematical optics to the proportions of the round brilliant cut and established what became known as the "ideal cut" — a set of proportions calculated to maximise the interplay of brilliance, fire, and scintillation. Marcel's work did not merely influence the trade; it restructured it, providing the theoretical framework that underlies modern cut-grading systems to this day.

Gabi Tolkowsky was born into this tradition in Antwerp, then as now one of the world's foremost centres of diamond cutting and polishing. He trained within the family craft from childhood, absorbing both the technical rigour and the patient, meditative discipline that serious diamond work demands. By the time he reached professional maturity, he had developed a reputation not only for technical mastery but for a willingness to engage with rough diamonds of exceptional complexity — stones that other cutters might have declined as too risky or too demanding.

The Centenary Diamond: Three Years of Deliberation

In 1988, De Beers announced the discovery of an extraordinary rough diamond at the Premier Mine in South Africa — a stone of 599 carats, colourless, and of exceptional internal clarity. Named the Centenary Diamond to mark the hundredth anniversary of De Beers, it was entrusted to Gabi Tolkowsky for fashioning. The commission was, by any measure, one of the most demanding assignments in the history of the craft.

Tolkowsky spent the first year doing nothing but studying the rough. A specially constructed, vibration-free studio was built beneath the Diamond Pavilion at the Premier Mine, and Tolkowsky worked there in conditions of extraordinary security and controlled environment. He used fibre-optic lighting to examine the stone's internal structure, mapping every inclusion, every grain boundary, every potential stress plane. The rough was irregular in form, and its internal characteristics — while ultimately consistent with an internally flawless grade — required meticulous planning to navigate. A single miscalculation could have introduced a fracture, destroyed a clarity grade, or wasted irreplaceable material.

The actual cutting and polishing proceeded over the following two years. Tolkowsky designed a modified heart-shaped brilliant cut with 247 facets — far exceeding the 58 facets of a standard brilliant — a geometry arrived at not for novelty but because the proportions of the rough demanded it. The finished stone weighed 273.85 carats. When De Beers unveiled it in 1991, the GIA graded it D colour and internally flawless: the largest diamond in the world to carry both designations simultaneously. The Centenary Diamond has been valued at figures exceeding one hundred million US dollars, though it has never been offered at public auction.

The process Tolkowsky followed with the Centenary Diamond has been documented in trade literature and in De Beers' own published accounts. What strikes observers is the proportion of time devoted to thought rather than action — a ratio that Tolkowsky himself has described as essential. In his view, the cutter's primary obligation is to understand the stone completely before touching it. The cutting itself, however technically demanding, is the execution of a plan formed in the mind.

The Golden Jubilee: The World's Largest Faceted Diamond

If the Centenary Diamond represents the pinnacle of colourless diamond cutting, the Golden Jubilee represents a different kind of triumph. Found at the same Premier Mine in 1985 — three years before the Centenary rough was recovered — the Golden Jubilee rough weighed 755.5 carats, making it the largest gem-quality rough diamond discovered since the Cullinan in 1905. It was, however, a very different proposition from the Centenary: brownish-yellow in colour, heavily included, and structurally complex in ways that made it genuinely hazardous to work.

De Beers initially used the rough as a test stone for new cutting tools and techniques, a role that itself speaks to the difficulty of the material. Tolkowsky was eventually commissioned to fashion it, and he transformed the unpromising rough into a cushion-shaped modified brilliant of 545.67 carats — a warm, cognac-brown colour that the trade describes as "fancy yellow-brown" or "fire rose cushion." The finished stone is the largest faceted diamond in the world by weight, surpassing the Golden Jubilee's nearest rival, the Cullinan I (also known as the Star of Africa, at 530.20 carats), by a significant margin.

The Golden Jubilee was presented to the King of Thailand, Bhumibol Adulyadej, in 1997 to mark the fiftieth anniversary of his accession — hence the name. It was blessed by the Pope, the Supreme Buddhist Patriarch, and the Supreme Islamic Imam of Thailand before being set into the Thai Royal Sceptre, where it remains part of the Thai Crown Jewels. The stone's journey from a difficult, brownish rough to a crown jewel of a sovereign nation is, in its own way, as remarkable as the Centenary's transformation from rough to record-holder.

Optical Philosophy and Working Method

Tolkowsky's approach to diamond cutting is distinguished by what might be called an optical philosophy: the conviction that the cutter's task is not to impose a predetermined form upon the rough, but to discover the form latent within it — the geometry that will allow the stone to express its maximum optical potential given its particular internal structure, colour distribution, and proportions. This is, in essence, the same intellectual tradition that Marcel Tolkowsky brought to his 1919 analysis, but applied at the level of individual stones rather than theoretical ideals.

In practice, this means that Tolkowsky's working method is characterised by extended periods of observation and planning, the use of computer modelling (which he adopted early and enthusiastically as the technology became available), and a willingness to design bespoke facet arrangements when standard geometries are not optimal for a particular rough. The 247-facet arrangement of the Centenary Diamond is the most dramatic example, but the principle applies across his body of work.

He has also been associated with the development of cutting techniques for particularly challenging rough — stones with unusual internal stress, irregular morphology, or colour zoning that requires careful orientation to produce the most desirable finished colour. His work on the Golden Jubilee, a stone that other cutters had found intractable, demonstrated that technical innovation and artistic vision could redeem material that conventional assessment might have written off.

Legacy and Influence

Gabi Tolkowsky's influence on the diamond trade operates at several levels. Most directly, his two record-setting commissions established benchmarks that have not been surpassed: no larger D-colour internally flawless diamond has been cut since the Centenary, and no larger faceted diamond of any description has been produced since the Golden Jubilee. These are records that may stand for generations, given the rarity of rough diamonds of comparable size and quality.

More broadly, his career has reinforced and extended the Tolkowsky family's contribution to the intellectual culture of diamond cutting — the idea that cutting is not a mechanical trade but a discipline requiring scientific knowledge, mathematical reasoning, and genuine artistic sensibility. In an era when much diamond cutting has moved toward automated and semi-automated processes optimised for yield and speed, Tolkowsky's work represents an insistence on the irreplaceable value of human judgement applied to individual stones.

He has been the subject of documentary coverage, museum exhibitions, and extensive trade-press documentation. The Centenary Diamond in particular has been exhibited publicly and has become a touchstone in discussions of what diamond cutting can achieve at its highest level. Tolkowsky himself has spoken and written about his methods, contributing to the broader gemmological literature on cut quality and optical performance.

Within the diamond trade, his name carries a weight that goes beyond celebrity. It represents a standard — of patience, of rigour, of respect for the material — that practitioners across the industry invoke when discussing what serious cutting looks like. That this standard is embodied in a living craftsman, rather than in a historical figure or a theoretical text, gives it an immediacy and an authority that purely historical precedents cannot match.

The Tolkowsky Name in Gemmological Context

It is worth noting, for the sake of clarity, that the Tolkowsky name appears in several distinct contexts within gemmological literature. Marcel Tolkowsky's 1919 ideal-cut proportions are the foundation of modern cut science. The "Tolkowsky brilliant" is sometimes used as a synonym for the ideal round brilliant. Various members of the extended family have been active in the Antwerp diamond trade across multiple generations. Gabi Tolkowsky's achievements are his own, but they are also the culmination of a family tradition that has shaped the discipline of diamond cutting more profoundly than any other single lineage.

When the GIA or auction-house catalogues refer to a stone as having been cut by Gabi Tolkowsky, the provenance carries with it the full weight of that tradition — a guarantee not merely of technical competence but of a particular intellectual and artistic seriousness that the family name has come to signify over more than a century of practice.

Further Reading

• GIA — The Centenary Diamond
• GIA — The Golden Jubilee Diamond
• GIA — Understanding Diamond Cut