 The sperm whale 's ivory @-@ like teeth were often sought by eighteenth- and nineteenth @-@ century whalers , who used them to produce inked carvings known as scrimshaw . Thirty teeth of the sperm whale can be used for ivory . Each of these teeth , up to 20 cm ( 8 in ) and 8 cm ( 3 in ) across , are hollow for the first half of their length . Like walrus ivory , sperm whale ivory has two distinct layers . However , sperm whale ivory contains a much thicker inner layer . Though a widely practised art in the nineteenth century , scrimshaw using genuine sperm whale ivory declined substantially after the retirement of the whaling fleets in the 1880s . Currently the Endangered Species Act and the Convention on International Trade in Endangered Species of Wild Fauna and Flora ( CITES ) , prevents the sales of or trade in sperm whale ivory harvested after 1973 or scrimshaw crafted from it . 
