It is curious indeed that with seekoei being the Afrikaans for hippo, that ‘sea cow’ should also be the origin of the Danish word hvalros for walrus, another source of ivory. Male and female walruses both develop large upper incisors which in the male can grow to over a metre in length.
In cross-section walrus tusk is the most distinctive of ivories. The outline is elliptical and irregular as the tusk is longitudinally grooved.
All tusks have an outer layer of cementum which is a bone-like material designed to help secure the tooth in the jaw. In walrus ivory this forms a distinctive layer which is less translucent than the dentine. The primary dentine, that lies below the cementum, is relatively featureless but as the tusk grows the central cavity of the tusk fills with a whorled secondary dentine that is unique to walrus ivory.
The vast majority of the Lewis Chessmen are made from walrus ivory and the characteristic cross-section of the tusk is visible on their bases. The whorled secondary dentine is sometimes visible on the backs of the chess pieces and where the carving has cut deep into the tusk.