The Cullinan VI Brooch is a platinum jewel in the British Royal Collection set with two polished stones derived from the celebrated Cullinan rough diamond — Cullinan VI, a marquise-cut diamond of approximately 11.5 carats, and Cullinan VIII, a cushion-cut diamond of approximately 6.8 carats — together with an emerald drop and a surround of smaller diamonds. Commissioned by Queen Mary in 1911, the brooch is among the most historically significant pieces of jewellery associated with the great Cullinan cutting project of 1908, and it occupies a distinctive position within the broader Delhi Durbar parure assembled for the Imperial Durbar held in Delhi in December of that year. Both principal diamonds are classified as Type IIa stones, a category defined by the near-total absence of nitrogen impurities and associated with the highest levels of optical transparency and colourlessness. The brooch is held in the Royal Collection and is periodically displayed alongside other Cullinan jewels.

The Cullinan Diamond and Its Division

The Cullinan rough was discovered on 26 January 1905 at the Premier Mine in the Transvaal, South Africa, by Frederick Wells, the mine's surface manager. Weighing 3,106.75 carats — approximately 621 grams — it remains the largest gem-quality rough diamond ever found. The stone was purchased by the Transvaal government and presented to King Edward VII in 1907 as a gesture of loyalty following the conclusion of the Second Boer War. The task of cleaving and polishing the rough was entrusted to the Amsterdam firm of Joseph Asscher & Co., then the foremost diamond-cutting house in the world. Work commenced in 1908 and ultimately yielded nine principal polished stones, designated Cullinan I through Cullinan IX, along with approximately ninety-six smaller brilliants and a quantity of polished fragments.

The nine principal stones range from the 530.20-carat Cullinan I — the largest polished white diamond in existence, now set in the Sovereign's Sceptre with Cross — down to the 4.39-carat Cullinan IX. Cullinan VI and Cullinan VIII, the two stones set in the brooch under discussion, represent the middle portion of this sequence in terms of size, but their optical qualities are in no way diminished by their relative weight. Both are assessed as Type IIa, a designation that places them among the rarest and most chemically pure diamonds known.

Cullinan VI and Cullinan VIII: Gemmological Character

Cullinan VI is cut in the marquise form — an elongated, boat-shaped outline with pointed ends — and weighs approximately 11.5 carats. The marquise cut, which became fashionable in the late nineteenth and early twentieth centuries, maximises the apparent size of a stone relative to its weight and flatters the elongated outline of a finger when worn as a ring; in a brooch setting, it provides a visually dynamic, directional element. Cullinan VIII is cut as a cushion, a form with rounded corners and a square or rectangular outline that was the dominant brilliant-cut shape prior to the widespread adoption of the round brilliant, and which retained prestige in royal and aristocratic jewellery well into the Edwardian era. At approximately 6.8 carats, it provides a harmonious counterpoint to the larger marquise without competing with it.

Both stones are Type IIa diamonds. In the classification system developed by Robertson, Fox, and Martin at the Cavendish Laboratory and subsequently refined by the Gemological Institute of America and other bodies, Type IIa diamonds contain no detectable nitrogen in any form — neither as isolated atoms (Type Ia) nor as aggregates (Type IaA or IaB). Because nitrogen absorbs in the ultraviolet and blue regions of the visible spectrum, its absence allows Type IIa stones to transmit light across a broader range, contributing to the exceptional colourlessness and brilliance for which the Cullinan diamonds are renowned. Type IIa stones constitute only a small fraction of all gem diamonds — estimates from GIA suggest approximately one to two per cent of gem-quality production — and the fact that the Cullinan rough yielded multiple large Type IIa polished stones underscores its extraordinary geological provenance.

Design and Construction

The brooch is set in platinum, the metal that had, by the first decade of the twentieth century, displaced silver and white gold as the preferred setting material for important white diamonds in European fine jewellery. Platinum's hardness, density, and resistance to oxidation made it ideal for the delicate millegrain and knife-edge settings characteristic of the Edwardian style, and its neutral colour allowed diamonds to appear at their most luminous without the faint warmth that even white gold can introduce.

The design incorporates an emerald drop suspended below the principal diamond elements. The use of emerald — deep green, saturated, and visually weighty — in combination with colourless diamonds was a well-established idiom in royal jewellery by the Edwardian period, offering chromatic contrast and a sense of luxuriant richness. The emerald drop introduces a pendant movement to the composition, giving the brooch a quality of animation when worn. The surrounding diamonds, smaller brilliants set in the platinum mount, serve to frame and amplify the two principal Cullinan stones without overwhelming them.

The brooch can be worn as an independent jewel or incorporated into the Delhi Durbar parure, a suite of jewels assembled for Queen Mary's attendance at the Delhi Durbar of 1911. This versatility — the capacity of a single piece to function both autonomously and as a component of a larger ensemble — was a hallmark of the finest Edwardian and early twentieth-century jewellery design, reflecting both the practical demands of royal ceremonial dress and the aesthetic preference for jewels that could be reconfigured to suit different occasions.

Queen Mary and the Delhi Durbar Parure

Queen Mary, consort of King George V, was among the most serious and knowledgeable collectors of jewellery in the history of the British monarchy. Her approach to the Royal Collection was systematic and acquisitive: she sought to consolidate historically significant pieces, to commission new jewels that would complement existing holdings, and to document the provenance and significance of stones already in royal possession. The Delhi Durbar parure — which includes the Cullinan VI Brooch alongside other pieces incorporating Cullinan stones — was assembled in the months preceding the 1911 Durbar, at which King George V and Queen Mary were proclaimed Emperor and Empress of India before an assembly of Indian princes and dignitaries at Delhi.

The Durbar of December 1911 was the only occasion on which a reigning British monarch attended such a ceremony in India in person, and the jewels worn by Queen Mary were chosen with deliberate symbolic intent. The Cullinan diamonds, derived from a stone presented to the British Crown by the Transvaal government, carried a specific political resonance in the context of imperial ceremony: they embodied the relationship between the Crown and its dominions. The Delhi Durbar parure, by incorporating Cullinan stones into a suite designed explicitly for the occasion, made this symbolism tangible and visible.

Queen Mary wore the parure at the Durbar and on subsequent state occasions. Photographs and portraits from the period document the ensemble, providing a visual record of how the individual pieces — including the Cullinan VI Brooch — were combined and worn. Queen Mary's careful stewardship of the Royal Collection ensured that the provenance and significance of each piece was recorded, and her practice of annotating jewellery inventories and correspondence with detailed notes has been invaluable to subsequent historians of the collection.

The Cullinan Stones in the Royal Collection

The nine principal Cullinan polished stones are distributed across several pieces in the Royal Collection, and their individual histories reflect the varied uses to which extraordinary diamonds have been put in royal ceremonial and personal jewellery. Cullinan I and Cullinan II are set in the Sovereign's Sceptre with Cross and the Imperial State Crown respectively, making them the most publicly visible of the group. Cullinan III and Cullinan IV are set in a brooch that Queen Mary wore with great frequency and which passed to Queen Elizabeth II. Cullinan V is set in a brooch that incorporates a heart-shaped diamond. Cullinan VII is set as a pendant. Cullinan IX is set in a ring.

The Cullinan VI Brooch occupies a particular position in this constellation because it combines two named Cullinan stones — Cullinan VI and Cullinan VIII — within a single jewel, and because its association with the Delhi Durbar parure gives it a specific historical context beyond the general significance of the Cullinan cutting. The brooch is not among the most frequently exhibited of the Cullinan jewels, but it is periodically displayed in exhibitions devoted to the Royal Collection and to the history of the Cullinan diamond.

Type IIa Diamonds: Scientific and Market Context

The Type IIa classification carries considerable significance in the contemporary diamond market as well as in the scientific literature. GIA's grading reports for Type IIa diamonds include a notation to this effect, and the designation is understood by sophisticated buyers as an indicator of exceptional purity. Several of the most celebrated large white diamonds in history — including the Koh-i-Noor, the Regent, and the Orlov — are Type IIa stones, and the concentration of Type IIa diamonds among the Cullinan polished stones is consistent with the Premier Mine's geological character: the mine has historically produced a disproportionate number of large, high-clarity, Type IIa diamonds, a fact attributed to the specific conditions of crystallisation in the kimberlite pipe from which it derives.

In the laboratory, Type IIa diamonds can be distinguished from other types by their infrared absorption spectra and by their behaviour under ultraviolet illumination. Some Type IIa diamonds exhibit a distinctive blue fluorescence under short-wave ultraviolet, a phenomenon that has been studied in the context of the Premier Mine's production. The optical properties of Type IIa stones also make them candidates for certain post-growth treatments — notably high-pressure, high-temperature (HPHT) treatment, which can improve the colour of near-colourless or slightly tinted Type IIa diamonds — but there is no suggestion that the Cullinan polished stones have been subjected to any such treatment. Their colour is the product of their natural formation.

Display and Public Access

The Cullinan VI Brooch, as part of the British Royal Collection, is not permanently on public display in the manner of a museum object with a fixed gallery location. The Royal Collection Trust manages access to the collection through exhibitions at the Palace of Holyroodhouse, Windsor Castle, and Buckingham Palace, and selected jewels are exhibited in the context of themed exhibitions or loan arrangements. The brooch has been displayed alongside other Cullinan jewels in exhibitions devoted to the history of the collection and to the story of the Cullinan diamond itself.

For those seeking to study the brooch in detail, the Royal Collection Trust's online catalogue provides documentation of pieces in the collection, and scholarly publications on the history of the Cullinan diamond — including accounts published in Gems & Gemology and in monographs on the Royal Collection — provide gemmological and historical analysis. The brooch is also documented in the records of Queen Mary's jewellery, which have been the subject of scholarly attention by historians of the British monarchy and of decorative arts.

Significance in the History of Gem Diamonds

The Cullinan VI Brooch is significant on several levels simultaneously. As a gemmological object, it presents two Type IIa diamonds of exceptional quality, cut from the largest gem-quality rough ever recovered, by the most accomplished diamond cutters of the early twentieth century. As a work of jewellery design, it exemplifies the Edwardian platinum-and-diamond aesthetic at its most refined, with the addition of an emerald drop that introduces chromatic complexity. As a historical document, it connects the Cullinan rough — a stone whose discovery and presentation to the British Crown were themselves historically charged events — to the Delhi Durbar of 1911, one of the most spectacular ceremonial occasions of the British imperial period. And as an element of the Royal Collection, it participates in a continuous tradition of royal jewellery that stretches back centuries and that continues to be worn and displayed by members of the British royal family.

Few jewels in any collection can claim this density of significance: geological, gemmological, aesthetic, historical, and dynastic. The Cullinan VI Brooch is, in this respect, a representative example of what the finest royal jewels can be — not merely ornaments, but objects in which the history of the earth, the history of craft, and the history of human affairs are simultaneously present.

Further Reading

• GIA — The Cullinan Diamond
• Royal Collection Trust — Online Collection