X-ray radiography revealed that the original design was executed by a technique of silvering called damasquinerie. Leaves of silver were hammered onto an iron core, then a design was incised through the silver sheet, and finally silver wires were pounded into the incisions.
A full account of this study is published by Barbara Oehlschlaeger-Garvey, et al., in chapter 10 of Ancient Technologies and Archaeological Materials, edited by S.U. Wisseman and W.S. Williams.