Bulla. A seal, usually lead and suspended by a cord attached to a document. The bulla bore a design formed by pressing an engraved seal die into the lead. The die was intaglio so the bulla would appear as a positive image. Papal bullas were lead seals affixed to religious papers; more important treaties bore silver (made by softening the silver first) or in very rare instances for the most important documents, gold bullas.
excerpted with permission from
For Artists, Makers, Collectors and Curators
COMPILED AND WRITTEN BY D. WAYNE JOHNSON
Roger W. Burdette, Editor