Institute For Ice Age Studies

Proboscidean tusks are merely specialized teeth (upper incisors), and are composed predominately of dentine. In contrast to many other ivories, mammoth and elephant tusks have a complex structure (Figure 6) formed by specialized cells know n as odontoblasts. These odontoblasts produce new dentine along the lining of the pulp cavity. As new dentine is produced, the odontoblasts migrate to the new surface of the pulp cavity, leaving behind processes known as dentinal tubules (MacGregor 1985) or so-called Schreger lines. These "radiate outward from the pulp cavity and incline obliquely towards the tip" of the tusk. The result, in transverse section, is a complex three-dimensional structure (Figure 7) that takes the form of arcs running counter to each other across the width of the tusk, and producing by their intersection what are frequently referred to as "engine-turnings" or the Schreger pattern.

In transverse section, this Schreger pattern cross-cuts broad concentric rings often referred to as laminae (Figure 8). These are actually growth interfaces between superimposed cones of ivory. In living tusk, the boundaries between these laminae are not areas of structural weakness, being bound together by the complex intersecting dentinal tubules composing the Schreger lines and by collagen fibres that fill the interstices between the dental tubules. However, upon dessication and accompanying deterioration of dentinal collagen, tusks tend to split or spall along these concentric boundaries, which are far more developed in the outer zones of the tusk's diameter. The inner core of the tusk, in the area surrounding the central nerve canal, is highly compact, homogeneous and virtually immune to such spalling. As a result, such inner ivory is exceedingly difficult to work with stone tools. It is perhaps no surprise then that in ivory-rich Aurignacian sites in SW France, this "core ivory" is abundantly represented in the waste products of tusk reduction.

Ivory has properties (color, luster, softness or warmth of touch) that set it apart from such media as bone and antler. However, these qualities can only be realized by means of polishing with fine abrasives. According to Ritchie (1969), modern ivory workers prefer fine metallic abrasives including jeweller's rouge, which is nothing more than hematite/red ochre. Indeed, SEM analysis of Aurignacian I ivory beads (White 1995b) revealed particles of red ochre embedded in the fine polishing striae on their surfaces. Moreover, large caches of red ochre have been recovered from two of the richest ivory-bearing Aurignacian sites in SW France: Abri Blanchard and Abri Castanet (Didon 1911; Peyrony 1935).