The Mohawk tribes were known for their mask carving, which is considered such a sacred art form that outsiders are still not permitted to view many of these masks. Beadwork and the more demanding porcupine quillwork are more common Mohawk crafts. The Mohawks also crafted wampum out of white and purple shell beads. Wampum beads were traded as a kind of currency, but they were more culturally important as an art material. The designs and pictures on wampum belts often told a story or represented a person's family.