German, late 16th century.
The ring is a size M UK / 6.75 US.
The bezel measures 1.1 x 1cm.
Weighs 3.4 grams.
This exceptionally rare ring was made as a betrothal ring during the late 16th century, the jeweller having recycled the antique intaglio which would have been engraved to represent a marriage in the ancient world. The reverse of the bezel is deeply engraved and shows traces of white enamel.
Chrome chalcedony which was known as plasma in the ancient world was widely used in jewellery and seals throughout the Roman Empire. The mineral disappeared from use in the ancient world in the 2nd century AD when the known deposits were mined out.