Among the Getty’s purchases at Christie’s New York, a c.16th century BC Minoan blue chalcedony tabloid seal cut with three swans – $95,000 (£73,000).

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The Los Angeles institution acquired 17 of the 40 Masterpieces in Miniature consigned for sale on April 29 by the heirs of Roman art dealer Giorgio Sangiorgi (1886-1965).

Highlights from the acquisition, in Switzerland since the 1950s, include two of the greatest-known ancient gems. A Roman intaglio portrait of Antinous, superbly engraved in black chalcedony c.130-138AD, sold at a record $1.75m (£1.35m) while a Roman amethyst ringstone with a portrait of Demosthenes, signed by the late 1st century BC court gem engraver Dioskourides, took $1.3m (£1m).

“The acquisition of these gems brings into the Getty’s collection some of the greatest and most famous of all Classical gems,” said Timothy Potts, director of the J Paul Getty Museum. “But the group also includes many lesser-known works of exceptional skill and beauty that together raise the status of our collection to a new level.”

All 17 gems, costing a total of $7.65m with premium, will be featured as part of a special exhibition opening at the Getty Center in December highlighting recent acquisitions. Following that, they will go on view at the Getty Villa.

For more on this sale, see the feature in this week's issue.