T here are precious few reminders of the lost Marlborough Gems at Blenheim Palace today. But once, the fabulous collection of more than 800 gems, painstakingly assembled by the cultured 4th Duke of Marlborough, aroused as much admiration and envy as the great palace in Woodstock itself.

As well forming the largest collection in Britain, the gems were recognised as remarkable works of art, some dating from the third century BC, some Roman and many from Renaissance Europe.

A famous portrait by Joshua Reynolds of the ducal family that hangs in the palace’s Red Drawing Room (pictured) offers colourful evidence of the Marlboroughs’ pride in their gems. The 4th Duke is shown clutching in his hand one of the cameos from his collection, while his heir, the Marquess of Blandford, holds one of the new red-morocco-bound gem cases, of which there were ten when the collection was catalogued in 1870.

Only five gems can still be found at the palace. The rest are spread all over the world, having been put on the market by the hard up 7th Duke, who in 1875, offered the whole collection of gems for sale at Christie’s in London.

The collection had initially looked like being kept together when it was snapped up by businessman David Bromilow, owner of colleries in the north-west, who viewed the gems as a sound investment. But when his daughter put them on the market once again at Christie’s, the gems were sold piecemeal.

Occasionally, the odd gem will appear in an auction house, like the cameo of a warrior sold last year in Paris for 97,000 Euros.

One man takes a close interest whenever one of the Marlborough gems comes to light.

He is Sir John Boardman, Oxford University Emeritus Lincoln Professor of Classical Art and Archaeology, who has undertaken a major study of the gems and set himself the task of trying to locate all of them, in what is turning out to be one of history’s great treasure hunts.

His search has led him from Malibu to Monaco. In the United States the main owners are in Boston and Baltimore, while there are several in the British Museum and the Victoria and Albert Museum, with one in Oxford’s Ashmolean.

So far he has managed to locate about 260 of the gems and has written a book, The Marlborough Gems, recently published by the OUP, a detailed academic study, which reveals how much is now known about the individual gems.

He was greatly helped by an archive of classical material put together by the late Oxford Professor John Beazley, which was acquired by the university’s Faculty of Classics in 1965. It contains catalogues and notebooks compiled for the duke, along with casts of all the gems providing researchers with precise copies of all the masterpieces in the collection.

Professor Boardman, who lives near the palace in Woodstock, said: “The 4th duke’s collection was the largest and most important of the 18th century English collections, internationally regarded by scholars and connoisseurs as the greatest of the private collections.”

But he fears the word ‘gems’ leads many to wrongly assume the collection was made up of precious stones, rather than exquisite works of art.

“They are hard semi-precious stones, which have been cut with intaglio figures and designs so that they can be set, usually in finger rings, and used as seals if you press them using wax or clay,” he explained. “And there are the more familiar cameos, which are much the same thing but with the figures cut in relief or layered stones, usually so they appear light on a dark background.

“The other important thing to remember is that they are all extremely small, many no more than one inch in length, few as big as two or three inches. But they are often set in expensive jewellery mounts or rings. ”

About a third of the collection can be traced back to the great 17th century collector Lord Arundel. When the famous Matuan collection was sold, Charles I moved in to snap up the paintings, while Arundel acquired the gems. (Arundel’s collection was taken to England in its fine painted Flemish cabinet, which Prof Boardman would dearly like to find. It was known to have been at Blenheim until the 19th century.) Miniaturist art has been practised in the western world from antiquity to the present day. Roman emperors are featured on the gems, along with a rich variety of classical compositions, portraits, heroic and biblical scenes and even animals (wild, domestic and mythical).

And for Prof Boardman each piece has its own tale to tell, from the moment of engraving to their last sale.

What a pity, though, that the old saga of a hard up English aristorcrat having to dispose of precious family assets, meant that the story of the miniature masterpieces that made up the Marlborough gems was never going to end in Woodstock.