C1770 Silver gilt ring with Glass Tassie cameo portrait of an 18th century gentleman, thought to be young Prince William Henry Duke of Gloucester, younger brother of King George III. Rings set with portrait miniatures of sovereign figures were quite popular and widely distributed.
A "Tassie" is a paste or glass copy of a cameo or intaglio. They were named for James Tassie, 1735-1799 who invented a technique for producing perfect copies of antique cameos and intaglios, which have the same detailing as a cameo but at a much lower cost. The portraits were modeled from life whenever possible and cast in white enamel then mounted upon a darker color background.
Set on blue guilloche enamel ground under domed glass. The ring is 1 1/4 inch tall and .75 inches wide (3.2 cm tall and almost 2 cm wide). It is a size 9 and weighs 12 grams.
More information about Tassies can be found on the Virginia and Albert Museum website.