The impression seal is a common seal that leaves an impression, typically in clay and less often in wax. In antiquity they were common, largely because they served to authenticate legal documents, such as tax receipts, contracts, wills and decrees. They are favorite topics of study because they were usually carved with important "themes" of the society that produced them, rather than with an ordinary signature. Others, less common, include the Egyptian, Levantine, or Canaanite scaraboid seals, and the metal stamp seal.