An affluent exile in Italy after 1791, Poniatowski was a passionate collector of antiquities and in later life commissioned an extraordinary series of about 2500 intaglios.
He encouraged the belief that the gems were ancient engravings (when in fact they were created by a group of contemporary gem-engravers in Rome who signed them with known or invented signatures) by publishing a catalogue of his gems with elaborate descriptions.
When, after his death, this collection was offered for sale by Christie's in London, connoisseurs and potential buyers were outraged to discover that the gems were 'modern', and the sale was unsuccessful.
Nevertheless, one John Tyrrell, not otherwise known as a collector, bought more than 1700 Poniatowski Gems, believing them to be genuinely ancient, as an investment and had numerous sets of plaster casts made from them which he published with an 'Explanatory Catalogue' in 1841.
It is only now that the gems are appreciated in their own right as fine examples of neoclassical gem engraving.
These 27 intaglios - carnelian, sardonyx and amethyst gems carved to depict classical scenes and offered in a fitted case - were offered at a jewellery sale at Bonhams Bond Street on September 19 and sold at £20,000, the lower end of their estimate.