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In page Sperm whale:

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The sperm whale's ivory-like teeth were often sought by 18th- and 19th-century whalers, who used them to produce inked carvings known as scrimshaw. 30 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 19th century, scrimshaw using genuine sperm whale ivory declined substantially after the retirement of the whaling fleets in the 1880s.[citation needed]