Prince Poniatowski and The Case of the Mistaken Gems
The most notorious case of modern gems being passed off as ancient was the case of the collection of Prince Stanlislas Poniatowski (1754-1833), a Polish prince, who settled in Rome and built up a large collection of gems starting with a small collection he had inherited from his uncle the King of Poland. The prince restricted access to the collection and it built up a mythic reputation. He published a catalog of it in 1830, and after his death it was sold at Christies in London in 1839, with collectors paying vast sums to acquire the gems. Within a few years though, doubts that had been percolating for years finally came to a head, when scholars could finally examine the gems. It became clear that the Prince had commissioned the 2600 gems from the foremost artists of his day, creating glyptich illustrations of Ovid, the myths of Hercules, and portraits of almost every ancient mythical or historic personage. Based on no ancient or contemporary works of art, these were original creations, if they were deceptively presented. By the mid-19th Century when the scandal had played its course, the mania for gems was essentially over, and gem carving declined in quantity and quality.
Burned by being duped by Poniatowski, scholars became ever more skeptical and this attitude has persisted to this day. One good thing however is that the “modern” gems were highly regarded as works of art on their own and many books on gem engraving such as Lippold and the Tassie impressions have it all, the ancient and the modern. This allows for one to educate ones eye, and chance upon cases where scholars may have been too conservative and put into the modern category a possible ancient piece or visa versa.