David discusses the legendary Beau Sancy diamond

In my 40 year career I presided over the sale of many famous gemstones, however, without doubt the most Royal and legendary was the Beau Sancy.

Peter Paul Rubens (1577-1640), The coronation of Marie de’ Medici in Saint-Denis, oil on canvas, 1620s

I was very fortunate indeed during my 40 year career at Sotheby’s to have presided over the sale of so many famous, record-breaking gemstones. All of them were individuals and each for me had a special character and unique attributes. But without doubt the most Royal and legendary among all these stones was the Beau Sancy.

What was it that made this diamond so very special, and for me totally unforgettable?

Firstly, weighing in at 34.98 carats, the Beau Sancy is not particularly huge – at least by the standards of today – but in the late 1500s when King Henry IV of France sent out agents to purchase the largest diamond they could find, this extraordinary stone was their main discovery. It should be remembered that the Golconda region of India was effectively the only source of diamonds known at this date, and so the stone was infinitely rarer than it would be today.

Secondly the colour of the stone is very slightly tinged with brown and not at all the ‘finest white’ which is so highly prized today. But size at this moment in history was of over-arching importance for the purpose in hand – to demonstrate the power of the French throne, since the diamond was to be the centrepiece of the crown which would be worn by Henry’s wife, Marie de’ Medici, at her coronation.

Finally, the cut of the stone and the unique arrangement of the facets, is very special indeed. It was designed specifically to fit the shape of the rough diamond crystal and thereby to preserve as much of the uncut weight as possible.

“Perhaps inadvertently, the cutter had also created a diamond of supreme presence, power and beauty, a diamond which haunts me to this day, and which is for me the very essence of royalty”

The Beau Sancy was first worn by Marie de’ Medici, depicted here in an oil on canvas from 1610 by Frans Pourbus the Younger (1569-1622), Marie de’ Medici Queen of France (1573-1642), the diamond sits at the top of her crown

The Beau Sancy was cut and polished towards the end of the 16th century, and exhibits one of the first attempts to liberate the ‘fire’ inherent in the stone. This property of diamond (dispersion) which is so familiar and so admired today is a function of the cut and was still pretty well unknown at this time due to the relative scarcity of stones for the cutters to practise on. It would take the discoveries in Brazil in the 1720s – and then later in South Africa and elsewhere from the second half of the 19th century, to release rough diamonds onto the market in sufficient quantities for the cutters in Europe to develop what we know today as the modern brilliant-cut in order for the full ‘fire’ to be released.

The Beau Sancy employed elements of the newly-developed ‘rose’ style of cutting, creating a totally unique facet lay-out which employed a myriad of triangular facets covering the entire surface of the crystal. This permitted the light which entered the stone to be reflected and dispersed, and broken up on the way into the colours of the rainbow. This ‘dispersion’ was a new phenomenon at this date. No other precious gem before this had been able to exhibit this extraordinary ability to transform light. It is this that made the Beau Sancy so utterly irresistible to Marie de’ Medici and it was to become the supreme solar symbol of her Monarchy.

Nicolas de Harlay, seigneur de Sancy (1546-1629), diplomat and financier, after whom the diamond was named. It is likely de Harlay acquired the stone in Constantinople

“The fact that the Beau Sancy was first worn by Marie de’ Medici as the principle stone and centrepiece of her coronation crown also indicates very clearly the importance of the diamond at this date as the supreme emblem of Monarchy”

On a symbolic level, since the time of Plato, diamonds had long been associated with the sun, our ”Daystar”, the dynamic centre of our cosmos – the source of all life and light. What other stone therefore could have been used to symbolise the parallel position and central role of the Monarch within his Kingdom? Indeed, later the same century, King Louis XIV would go a step further and call himself ”Le Roi Soleil”, the Sun King.

The Beau Sancy, a modified pear rose-cut diamond, depicted here in diagrammatic form by Thomas Cletcher, 1644. The Dutch jeweller, goldsmith and dealer, from The Hague, was involved in several transactions of jewels of historical importance.

At the moment of coronation, the crown is lowered onto the Monarch’s head from ‘above’ by the representative of the Church and Spiritual Authority. In doing so the lesser, Temporal Authority is vested in the King or Queen. It is not difficult to imagine the scene at the Abbey of St Denis, Paris, on the 13th May 1610. The vast space is packed with a huge congregation, their voices reduced and hushed to a whisper as they eagerly participate in the spectacle. All eyes are focused on the kneeling Marie de’ Medici as her crown is gently lowered onto her head. At the apex of the crown, surrounded by other, lesser diamonds, the Beau Sancy, proud and magnificent, captures and throws back the light of a thousand candles and the glancing rays of the midday sun.

“I think I can be forgiven for being so much in awe of this remarkable gemstone from the first moment it rested in my palm.”