Mother-of-pearl, jet coral and amber were selected by craftsmen for their beauty, durability and rarity. These materials often occurred in a particular geographical region. Coral for example was prevalent in Sicily and amber along the Baltic coast. Many of the religious items were portable, as were the small portraits. They were often made locally and then taken elsewhere. Pilgrims from all over Europe bought the jet images made in Santiago de Compostela. This relief was perhaps once part of a pendant. Many other jet images of St Anthony are known, some very close to the present piece. St Anthony of Padua seems to have enjoyed some popularity with the carvers of Santiago.
In structure jet is a particularly dense type of coal, and can be carved and polished. Medicinal and indeed magical qualities were thought to be inherent in the substance from earliest times. Jet is found in different parts of Europe (as well as North America), but the two richest regions are the Asturias in northern Spain, and Whitby, Yorkshire, in North East England.