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Identification of Elephant Ivory

Discussions and analysis of Elephant Ivory
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souldeep
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Identification of Elephant Ivory

Postby souldeep » Mon Mar 28, 2016 3:49 pm

Identifying Elephant Ivory - Loxodonta africana and Elephas maximus

Elephant tusk ivory comes from the two modified upper incisors of extant order (Proboscidea).

An African elephant tusk can grow to 3.5 meters in length. Enamel is only present on the tusk tip in young animals. It is soon worn off and not replaced. Whole cross-sections of proboscidean tusks are rounded or oval. Dentine composes 95% of the tusk and will sometimes display broad concentric bands. Cementum, which can be thick in extinct genera, covers the outside of the tusk. Cementum can present a layered appearance, particularly in mammoth.

Polished cross-sections of elephant ivory dentine display uniquely characteristic Schreger lines. Schreger lines are commonly referred to as cross-hatchings, engine turnings, or stacked chevrons. Schreger lines can be divided into two categories. The easily seen lines which are closest to the cementum are the outer Schreger lines. The faintly discernable lines found around the tusk nerve or pulp cavities are the inner Schreger lines. The intersections of Schreger lines form angles. These Schreger angles appear in two forms: concave angles and convex angles. Concave angles have slightly concave sides and open to the medial (inner) area of the tusk. Convex angles have somewhat convex sides and open to the lateral (outer) area of the tusk. Outer Schreger angles, both concave and convex, are obtuse in extant proboscidea.

A photocopy machine is used to capture Schreger angles from mammoth and elephant ivory cross-sections. The cross-section is placed on the glass plate of a photocopy machine. A blue photocopy transparency sheet may be placed between the object and and the glass plate to enhance the detail of the photocopy. Enlargement of the photocopy may also improve the image and facilitate the measurement process.

After a photocopy of the ivory cross-section has been obtained, Schreger angles may be marked and measured. Use a pen or pencil and a ruler to mark and extend selected outer Schreger angle lines.

NOTE: Only outer Schreger angles should be used in this test.

Once the angles have been marked and extended, a protractor is used to obtain an angle measurement. Several angles, including both concave and convex angles, should be marked and measured. Once the angles have been marked and measured, calculate the angle average.

Because specimens from both extinct and extant sources may present angles between 90 degrees and 115 degrees in the outer Schreger pattern area, the differentiation of mammoth from elephant ivory should never be based upon single angle measurements when the angles fall in this range.

When averages are used to represent the angles in the individual samples, a clear separation between extinct and extant proboscideans is observed. All the elephant samples has averages above 100 degrees.

elepschr.jpg

Elephant ivory will not display intrusive vivianite discolouration in its natural state. It is of interest to note that when the discolouration is barely perceptible to the eye, the use of a hand-held ultraviolet light source causes the blemished area to stand out with a dramatic purple velvet-like appearance. Even if discoloured, elephant ivory will not have the characteristic fluorescence of vivianite.
Piglet: "Pooh?" Pooh: "Yes, Piglet?" Piglet: "I've been thinking..." Pooh: "That's a very good habit to get into to, Piglet." - A.A. Milne.

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