The Mughal Mirror Diamond Necklace is a remarkable survival from India's jewel-strewn past. Its five pendant diamonds come from the famous mines of Golconda in the Deccan. Their quality is such that it is hard to believe that they did not enter a royal treasury on their discovery, for the emperors and princes who vied for control over the Golconda mines always claimed the best stones for themselves.

The skilful table-cut – designed to emphasize the beauty of the stones without sacrificing their size – is called parab or 'flat' in India. It dates their fashioning to the 16th or 17th centuries, the glory days of the Mughal Empire. Numerous portraits survive of Mughal emperors wearing such magnificent diamonds. The central stone, at 28 carats, is the largest table-cut diamond known to have survived. It must surely have once adorned a royal breast.

The stones' setting (and the addition of the fluted emerald drops) is later than their cut, but it, too, has a Mughal feel. The curved sections between the projections holding the stones echo the shallow pointed arches of iconic Mughal buildings such as Humayan's Tomb and the Taj Mahal. It is lighter and less intrusive than India's traditional kundan settings, whereby a stone was embedded in soft, malleable gold. Kundan was well suited to stones for which brilliance could be enhanced by foiling, but these are diamonds of superb clarity and limpidity. They need no foils and kundan might have masked their beauty.

It is a marvel that the diamonds have survived together and in this setting for so long. As early as the 1780s, India's princes were exploring western decorative traditions, importing European mirrors, chandeliers and furniture in surprising quantities. By 1850, this trend had stretched to jewelry and adventurous maharajahs were experimenting with new, lighter settings and western-style faceting. Some, such as Khande Rao, the fabulously rich Gaekwar of Baroda, cut straight to the chase and started buying headline-grabbing diamonds from foreign mines. In the late 1860s he snapped up two Brazilian diamonds that had been shown at the International Exhibition in London in 1862: the 128.8-carat Star of the South, for which he paid £80,000 and, at half that price, the 76.5-carat English Dresden. He had these set in a necklace formed of three rows of faceted diamonds – 90 stones in total.

In 1870, this necklace was inherited by Khande Rao's brother and successor, Malhar Rao. He added a few more diamonds to it, but he evidently had some to spare, for he was subsequently accused of lacing his British adviser's breakfast sherbet with a lethal mix of arsenic and ground diamonds. Charged with conspiracy to murder, he narrowly escaped the death penalty, but was forced to abdicate. He had no heir and Khande Rao's widow adopted a son to succeed him. Sayaji Rao III (opposite) was 12 years old, illiterate and unworldly, when he was plucked from his home and placed on Baroda's throne. In November 1875, ablaze with the riches of the state treasury, he was presented to the Prince of Wales, who marveled that he had but six months before been "running about the streets adorned with the most limited wardrobe".

Baroda and other big states such as Hyderabad were innovators in importing new jewels, but princes from the smaller states were not far behind. In 1875 Mahendra Singh of Patiala took an accessorizing short-cut not open to most men when he secured a necklace of diamond brilliants from the Empress Eugénie's collection in time for an audience with the Prince of Wales. It is a measure of the sartorial latitude allowed to maharajahs that European observers at the meeting were struck more by the caliber of the stones than the fact that they had been set for a woman. Mahendra's son and successor, Rajendra Singh, revealed a similar flexibility when he commissioned a diamond turban ornament that was, in all but size, a woman's tiara.

While other princes did not go so far as to import foreign stones or jewels, few could resist the temptation to experiment with new flamboyant settings. This includes even the rulers of the ancient, traditionally conservative Rajput states. A photograph of Raghubir Singh, Maharao of Bundi (opposite, far right), survives from around 1897. Peeping out from beneath the startling coiffure of his beard is a magnificent necklace of five very large flat diamonds, laden with emerald drops. But this has nothing of the sparse elegance of the Mirror Diamond Necklace. Each of the large diamonds radiates smaller ones and the whole is linked together by gold wirework. Photographs of his venerable father, who reigned for 68 years, show no such necklace. Indeed, Ram Singhji was notably austere in his attire, but he was reported to wear a great 'hand of gold' set with flat diamonds in his headdress, which his son may have raided to create his star piece.

Meanwhile, enterprising European jewelers began searching out stones and commissions among the Indian princes. In 1895, for example, Queen Victoria's jewelers, the Benson brothers, were credited with persuading British and French women of the desirability of the old cabochon emeralds they had been buying up in India. This quickly turned into a two-way traffic, as Indian princes traveled to Europe in search of modish novelty and liberation from the constraints of British overlordship at home. French jewelry houses were the beneficiaries of this trend. In the 1910s and 1920s, many princes commissioned new settings of their best stones from Boucheron, Cartier, Chaumet and Mauboussin. Few exhibited quite the level of Francophilia as Jagatjit Singh of Kapurthala, who built his own Louis XVI-style château in the foothills of the Himalayas, but there were enough commissions for the jewelry houses to regard the princes as a useful source of stones and an exotic form of publicity.

One of the most enthusiastic patrons of the French houses was Bhupindar Singh, Maharajah of Patiala. He matched the roving appetites of his grandfather and father. He was also one of Britain's most loyal princes – which rather taxed his British minders who were charged with subtly reining in his expenditure. He constantly bought new stones, including fancy colored diamonds by the fistful, and he delighted in having his old jewels reset. Along with the maharajas of Kapurthala and Indore, he was one of the first princes to be seduced by platinum settings. Platinum's density and robustness enables settings to be minimized, leaving the stones to shine for themselves, but for an Indian prince this meant turning his back on the ancient beliefs that linked gold with royal and divine power.

By 1928, Bhupindar Singh was ready to make this break, and in spectacular manner. On 2 August, he appeared in Boucheron's showroom on Place Vendôme, accompanied by a dozen pink-turbaned bodyguards bearing six trunks of jewels. Louis Boucheron's staff reeled at their contents: pearls and rubies by the hundreds, diamonds by the thousand, and, most extraordinary of all, 1,432 large emeralds totalling 7,800 carats. Bhupindar Singh wanted them all reset, and placed orders for 149 new jewels that day alone. The settings were to be as modern as possible, while at the same time conforming to traditional Indian usage. Boucheron's designers worked around the clock, but even then they had to farm out some of the smaller pieces to other firms. Imagine their indignation when, just a few months later, rival house Cartier announced an exhibition to show off their new settings of the 'crown jewels of Patiala'. Cartier, it seems, had been working on an equally large commission since 1925. Remarkably, the gems that Bhupindar Singh's bodyguards had lugged along to Boucheron comprised only a fraction of his hoard.

Both houses created some spectacular pieces for Bhupindar Singh, but it is one of Cartier's designs that evokes the Mirror Diamond Necklace – a large bib-like piece that showcased more than 70 old table-cut diamonds. It was a magnificent combination of old and new, with a traditional cord tie, but set in minimal platinum with the old diamonds that were beautifully enlivened by hundreds of small brilliants.

Patiala is an extreme example, but few of the very best stones in India's royal storehouses escaped resetting during
the 19th and early-20th centuries. How did the Mirror Diamond Necklace survive with its beautiful old setting intact? Has it been tucked away in the treasury all these years, or did it perhaps leave India before the craze for resetting took off? This is a strong possibility. The waning of the Mughal Empire and the rise of British power in India occasioned the dispersal of many royal jewel collections. One of the last and most suggestive of these episodes concerns the jewels of the north Indian state of Oudh, which largely disappeared from view after their spoliation. In 1856, the British forced the abdication of the last King of Oudh, Wajid Ali Shah, accusing him of incompetence and misrule. He was pensioned off and allowed to take his personal jewelry with him to a gilded exile in Calcutta. But many of the state jewels remained behind in his palaces at Lucknow, which was the scene of some of the fiercest fighting during the Great Rebellion of 1857-1858.

On 14 March 1858, as the British fought to regain control of the city, troops smashed their way into the Kaisarbagh, a palace built by Wajid Ali Shah himself. William Howard Russell, war correspondent of The Times, followed them and was astonished by what he saw. One soldier smashed open a solid silver box and held up a diamond armlet dripping with emeralds and pearls. He offered it to Russell for a hundred rupees, but, to his lasting regret, Russell had no money with him. He heard later than an officer had given £7,000 for it.

What happened to those jewels? Newspaper reports suggest they were widely dispersed. In March 1860, Messrs Dowell and Lyell auctioned a 'casket of Oriental gems' in Edinburgh which had clearly come from Oudh. Among the items was a rock-crystal bowl said to be Wajid Ali Shah's 'soup bowl' and a portrait of the deposed king. There were also flat diamonds set in gold, large emerald drops, and hundreds of pea-sized pearls. Two years later, the Secretary of State for India asked for a host of royal Indian jewels, including turban and arm ornaments studded with flat diamonds and festooned with emeralds, to be sent to auction. Again, the source was most likely Oudh. Such sales can have accounted for but a fraction of Oudh's wealth, but they show that even at this early period there were collectors in Europe who prized Indian jewels as opposed to Indian stones; in both of these cases the buyer was a Rothschild.

There was nothing unusual about this process, of course. For millennia, wars had occasioned the redistribution of India's extraordinary gem wealth, within the country and abroad. When Nadir Shah sacked Delhi in 1739, the plundering continued for weeks and the Persian treasury was immeasurably enriched. During the East India Company's ascendancy in India both formal prize-taking and the drunken plunder described by Russell were so common that the British also raided a word from the Hindi language to describe it: 'loot' comes from the Hindi verb lutna, meaning 'to plunder'. Ironically, if the Mirror Diamond Necklace did leave India by such a violent route, it would mean that a rare piece of Mughal jewelry history had survived precisely because of a catastrophic act of destruction.

Katherine Prior is author of The Maharajahs' Jewels. Her next book, Good Hands: 250 Years of Craftsmanship at Swaine Adeney Brigg, is published in June.

The Mughal Mirror Diamond Necklace is offered by Bonhams for sale
by private treaty at $20m. For more details, please contact Jean Ghika +44 (0) 20 7468 8282,

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