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Identification of Marine Ivory

Discussions, identification and analysis of the different types of Marine Ivory
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souldeep
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Identification of Marine Ivory

Postby souldeep » Tue Apr 26, 2016 2:41 pm

The Ivories, used within netsuke and referred to as marine, are most likely to have been sourced from a Whale, Walrus or Narwhal.


WALRUS - Odobenus rosmarus

Walrus tusk ivory comes from two modified upper canines. The tusks of a Pacific walrus may attain a length of one meter. Walrus teeth are also commercially carved and traded. The average walrus tooth has a rounded, irregular peg shape and is approximately 5cm in length.

The tip of a walrus tusk has an enamel coating which is worn away during the animal's youth. Fine longitudinal cracks, which appear as radial cracks in cross-section, originate in the cementum and penetrate the dentine. These cracks can be seen throughout the length of the tusk. Whole cross-sections of walrus tusks are generally oval with widely spaced indentations. The dentine is composed of two types: primary dentine and secondary dentine (often called osteodentine). Primary dentine has a classical ivory appearance. Secondary dentine looks marble or oatmeal-like. This type of secondary dentine is diagnostic for walrus tusk ivory.

The dentine in walrus teeth is mainly primary dentine. The centre of the tooth may contain a small core of apparent secondary dentine. The dentine is completely surrounded by a cementum layer. Enamel may or may not be present according to the extent to which the tooth has been carved or worn. A cross-section of a walrus tooth will show very thick cementum with prominent cementum rings. Concentric rings in walrus teeth are due to hypercementosis. The dentine is separated from the cementum by a clearly defined narrow transition ring.

walrtus.jpg

C - Cementum
PD - Primary Dentine
SD - Secondary Dentine


SPERM WHALE AND KILLER WHALE - Physeter catodon and Orcinus orca

Sperm whale teeth can be quite large. The average height is approximately twenty centimetres. Killer whale teeth are smaller. Both species display conically shaped teeth with a small amount of enamel at the tips. The rest of the tooth is covered by cementum. Whole cross-sections of killer whale and sperm whale teeth are rounded or oval (figure).

In addition, killer whale teeth show two slight peripheral indentations. The dentine is deposited in a progressive laminar fashion. As a result of this laminar deposition, killer and sperm whale teeth will show prominent concentric dentine rings in cross-section. Killer whale teeth may also display a faint rosette pattern in the dentine cross-section. The dentine is separated from the cementum by a clearly defined transition ring.

spermhor.jpg


NARWHAL - Monodon monoceros

The narwhale is a rarely seen arctic whale. The male of this species has a single left tusk that is a modified upper incisor. The tusk is spirally twisted, usually in an counter-clockwise direction. In a mature specimen the tusk can be from two to seven meters long.

Enamel may be present at the tip of the tusk. The cementum frequently displays longitudinal cracks which follow the depressed areas of the spiral pattern. As a result, narwhal tusk cross-sections are rounded with peripheral indentations. The cementum is separated from the dentine by a clearly defined transition ring. Like killer and sperm whale teeth, the dentine can display prominent concentric rings. The pulp cavity extends throughout most of the length of the tusk giving cross-sections a hollow interior.

narwhal.jpg

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