From the recovery after the Irish Potato Famine in the 1840s to the booming Celtic Tiger of the 1990s, a revival of the ancient traditions of Celtic jewelry have become a part of how the Irish, as well as the Scots, Welsh and other Celts have expressed their cultural identity. Usually the story of this tradition focuses on very old prototypes, the museum pieces turned up by archaeologists or the legend of the original Claddagh ring. In our imagination, we connect the popular Celtic jewelry of today with the distant past. But that link with the ancient style was very much influenced by what...