WOW!  Talk about appreciation.  An intaglio from the first century BC was auctioned by Sotheby’s in December 2016 with an estimate of $10,000 to $15,000; it was sold to the Getty Museum for just over $500,000. 

The listing is still available at http://www.sothebys.com/en/auctions/ecatalogue/2016/old-master-sculpture-l16233/lot.88.html

The provenance or history of the intaglio provided by Sotheby’s includes its being a part of the Marlborough Gems, its “acquisition” by the Nazis, and its recovery by the so-called “Monuments Men”.