The Centenary Diamond is one of the most technically accomplished and gemologically significant diamonds in recorded history. Weighing 273.85 carats in its finished form, it is graded D colour and internally flawless by the Gemological Institute of America — placing it at the absolute summit of both the colour and clarity scales. It ranks among the largest diamonds in the world to achieve those combined grades, and its cutting, which consumed nearly three years and employed computer modelling alongside laser technology, represents a watershed moment in the art of fashioning exceptional rough. The stone was unveiled by De Beers in May 1991 to mark the centenary of the company's founding, and it has remained in private hands ever since.

Discovery and Rough Crystal

The rough from which the Centenary was fashioned was recovered in 1986 at the Premier Mine (now known as the Cullinan Mine) near Pretoria, in South Africa's Gauteng province. The Premier Mine has an extraordinary pedigree in the annals of diamond history: it is the source of the Cullinan Diamond — the largest gem-quality rough diamond ever found, at 3,106.75 carats — as well as numerous other notable stones. The Centenary rough weighed approximately 599 carats and was described at the time as one of the finest large crystals the mine had produced in decades. It was recovered in the recovery plant rather than by direct mining, which spared it from the mechanical damage that sometimes affects crystals extracted by blasting.

The rough was kept secret for two years while De Beers assessed its potential. Its exceptional colour and transparency made it clear that an extraordinary cutting project lay ahead, and the decision was taken to dedicate the stone to the company's centennial celebrations.

Cutting and Faceting

The cutting of the Centenary Diamond was entrusted to master cutter Gabi Tolkowsky, a member of the celebrated Tolkowsky family whose contributions to diamond cutting theory span generations. Tolkowsky — nephew of Marcel Tolkowsky, whose 1919 mathematical treatise established the proportions of the modern round brilliant — brought both inherited expertise and a highly individual creative sensibility to the project.

Work began in a specially constructed, dust-free, climate-controlled vault at De Beers' research facility in Johannesburg. The process lasted approximately three years, from 1988 to 1991. Tolkowsky and his team used advanced computer modelling to map the rough crystal's internal structure, identifying inclusions and planning a cutting strategy that would maximise both yield and optical performance while eliminating or isolating any clarity characteristics. Laser technology was employed in the initial cleaving and shaping stages — a relatively novel application at the time for a stone of such consequence.

The finished diamond is fashioned as a modified heart-shaped brilliant, a form that Tolkowsky developed specifically for this stone rather than applying any standard template. It carries 247 facets in total: 164 facets on the crown and girdle, and 83 on the pavilion. The girdle itself is faceted and bears an inscription. The result is a stone of exceptional optical complexity, designed to maximise the interaction of light across its unusual outline while preserving the integrity of the heart shape at every viewing angle.

Gemological Characteristics

• Finished weight: 273.85 carats
• Colour grade: D (colourless) — the highest grade on the GIA scale
• Clarity grade: Internally Flawless (IF) — no internal characteristics visible under 10× magnification
• Cut: Modified heart-shaped brilliant
• Facets: 247
• Origin: Premier Mine (Cullinan Mine), Gauteng, South Africa
• Grading laboratory: Gemological Institute of America (GIA)

The combination of D colour and internally flawless clarity in a stone exceeding 100 carats is exceptionally rare; in a stone of 273.85 carats it is virtually without parallel in the documented record. The GIA grading report confirmed these grades following the stone's completion in 1991, lending institutional authority to what De Beers had described during the cutting process.

Unveiling and Public Exhibition

The Centenary Diamond was formally unveiled at the Tower of London on 1 May 1991, during a gala event marking De Beers' centenary. The choice of venue was deliberate: the Tower of London houses the Crown Jewels, and the association placed the Centenary in a lineage of historically significant diamonds displayed in that setting. The stone was exhibited publicly for a period alongside other De Beers treasures, drawing considerable attention from the press and the gemmological community alike.

Its unveiling coincided with a period of intense public and trade interest in exceptional diamonds, and the Centenary was positioned by De Beers not merely as a corporate anniversary piece but as a demonstration of what the company's mines and technical resources could produce at their finest.

Provenance and Current Ownership

Following the period of public exhibition, the Centenary Diamond passed into private ownership. The identity of the owner or owners has not been publicly disclosed, and the stone has not appeared at public auction. Its estimated value has been cited in various contexts at figures ranging into the tens of millions of pounds sterling, though no verified sale price is on record. The absence of a public transaction means that, unlike the Hope Diamond or the Cullinan fragments, the Centenary's market value remains a matter of informed estimation rather than documented fact.

Its current whereabouts are unknown to the public record. It is not on display in any museum or royal collection, and it does not appear in the inventories of any known institutional holding.

Significance in the Diamond World

The Centenary Diamond occupies a distinctive position in the hierarchy of famous diamonds. Unlike many celebrated stones whose fame rests primarily on historical narrative — conquest, curse, royal association — the Centenary's renown is grounded almost entirely in gemological merit. It is not the largest diamond ever cut, nor does it carry the dynastic weight of the Cullinan or the Koh-i-Nûr. What distinguishes it is the combination of superlative grading standards, extraordinary size, and the technical ambition of its cutting — a project that pushed the boundaries of what was then possible in the fashioning of exceptional rough.

Gabi Tolkowsky's modified heart shape, developed specifically for this stone, also contributed to a broader conversation in the trade about the possibilities of non-round brilliant cuts for large, high-quality diamonds. The use of computer-aided design and laser technology in its preparation anticipated practices that would become standard in high-end diamond cutting over the following decades.

For gemmologists, the Centenary serves as a reference point for what D/IF grading means at the extreme upper end of the size range — a reminder that the GIA scale, designed to be universal, applies with equal rigour to a 0.50-carat round brilliant and to a 273.85-carat modified heart of world-historical significance.

Further Reading

• GIA — Famous Diamonds Overview
• GIA — History of Famous Diamonds