Plaque with Marking of the Door with the Letter Tau
The image here had its origin in the Passover, when Moses ordered the elders of Israel to mark the houses of the Israelites with the blood of a slain lamb to protect their households. For Christians, the tau came to be seen as an emblem of God's protection. In the enamel, the mark is placed on a building resembling a medieval church, with a prominent cross on the roof.
Champlevé is an enameling technique in which troughs or cells are carved, etched, die struck, or cast into the surface of a metal object, and filled with vitreous enamel. The piece is then fired until the enamel fuses, and when cooled the surface of the object is polished. A frequent use of champlevé technique is first seen in early Celtic art in Europe, from the 3rd or 2nd century BC. The name comes from the French for "raised field", meaning background, though the technique in practice lowers the area to be enameled rather than raising the rest of the surface. The technique has been used since ancient times and in Romanesque art its potential was fully used, decorating caskets, plaques, and vessels.