In its strict definition, the term "ivory" refers the tusks of elephants, but it is often stretched to include the tusks of other animals such as the hippopotamus and walrus. It is sometimes confused with, but does not include, bone. Tusks are elongated incisors composed of a substance known as dentine, which consists of numerous tiny tubes. Unlike bone, dentine doesn't contain blood vessels, which are apparent in bone as little black specks. Identifying the different kinds of ivory requires an eye for subtle details.
Determine the item's shape. Identify elephant ivory by looking first for a distinctive elephant tusk shape in larger pieces--i.e., a slender, sabre-like curve. The piece should have a faint, longitudinal grain which appears and disappears as you turn it in the light. Turning to the base, you should see a cage-like effect of intersecting lines, as well as a series of faint concentric shaded rings, like the rings of a tree. In the centre of these rings is a knot-like formation, which is the nerve canal. On fine pieces of Japanese ivory such as standing figures or "okimono," this is often covered with an inset label giving the artist's name.
Examine the base. Recognise walrus ivory by turning to the base. In contrast to elephant ivory, walrus ivory has a granular inner core. You will also frequently see a slight ring of discolouration just within the outer edge. Walrus ivory was often used for smaller carvings such as Japanese netsuke (an item that fitted on the sash around a Japanese person's waist) and in the West for scrimshaw, the crudely scratched decorative pieces created by sailors on their voyages.
Spot hippopotamus ivory by looking for either a triangular or a circular base, depending on whether the piece comes from a canine or an incisor--the two kinds of hippopotamus teeth most commonly used. As hippopotamus ivory is very hard, it is mainly used for items which need only shallow carving, such as buttons and inlay. Flat sections of ivory can be set into other objects such as trinket boxes.