By Max Colchester | Photography by Felix Odell for WSJ. Magazine ITTAI GRADEL, an academic–turned–gem dealer in Denmark, was trawling eBay a decade ago when he thought he had stumbled across a gold mine.On his screen, Gradel saw a seller called Sultan1966 advertising a glass gem from the 19th century. Gradel immediately recognized it as something much more valuable: an agate Roman Medusa cameo from the second century, featuring the mythical Gorgon with snakes as hair. He snapped it up for £15 plus postage, then turned around and sold it to a collector for a couple of thousand pounds. Copyright ©2023 Dow Jones & Company, Inc. All Rights Reserved. 87990cbe856818d5eddac44c7b1cdeb8