Ivory has been used in the production and ornamentation of beautiful objects since earliest times. Ivory carvings have been found in the mounds and ruins of ancient cities mentioned in the Bible, and examples of carving representative of the early Assyrian and Egyptian dynasties can be seen in many modern museum. Ivory has held an honored place in the adornment of the places of the great of all ages, particularly for wall and ceiling inlay and small decorative objects. Its whiteness, warmth and purity fitted it for use as a distinctive ornament of royal dignity, and was especially appropriate or the scepters and thrones of rulers and potentates. In the Bible there is a reference to the great ivory throne overlaid with pure gold that was made for King Solomon by the skilled workmen of Hiram, King of Tyre. In the Song of Solomore the expressions "ivory overlaid with sapphires" and "tower of ivory" are still used today in the litany of the Catholic Church. Outstanding examples of ivory sculpture repose in great public and private collections throughout the world; although not numerous, some provide outstanding examples of sculptural artistry. The word ivory originated with the Latin "eboreus", and came to us through the old French "yvoire."
The term ivory may be confined to the material that comprises the tusk of the elephant, although similar materials produced by several other animals are usually considered ivory as well. Both male and female African elephants furnish good-sized tusks; in India, on the other hand, the female has very small tusks. In Ceylon, few elephants, either male or female, grow tusks. When elephants are kept in captivity, the tusks are shortened occasionally by the keeper; the product, however, is not as valuable as that from the wild animal. Elephant tusks, which are the upper prolonged incisor teeth, often attain enormous development, some measuring eight to ten feet in length and weighing as much as 180 pound. The curvature from the root to the extreme point is sometimes equal to half a circle. They are hollow to about half their length, being formed of layers of dentine on a vascular pulp. The thin outer layer consists of a slightly harder coating of enamel. The enamel is eliminated during carving, since it is too thin to be used to advantage.
The composition of ivory is essentially the same as the hard, bony substance of which most teeth are composed. It consists of an organic matrix that is richly impregnated with calcareous salts and permeated with an immense number of extremely fine tubes, starting from the pulp cavity and radiating outward in all directions. The substance is very dense and the pores are close and-compact and filled with an oily or waxy solution that contributes to the beautiful polish and makes it more supple and amenable to the worker's tool than, for example, the more refractory marble and bone.
Ivory, which varies from translucent to opaque, is produced by the following animals:
- African Elephant
The finest and most beautiful ivory, which is known as green ivory, is from the vicinity of Pangani, in Tanganyika Territory. The type called cape ivory is softer, sometimes yellowish, and occasionally a "dead white" color. Material from Senegal and Ethiopia is similar but less perfect and valuable.
- Asiatic Elephant
Ceylonese ivory is usually very white, but the most esteemed is a pale rosy white. That from Thailand resembles the Ceylon variety. Bombay ivory is an inferior type.
- Mammoth and Mastodon
The tusks of these prehistoric animals, which have been preserved in the earth for thousands of years, produce fossil ivory. Only about 15% of the material found is useable and fairly good quality. Odontolite is a name given to fossil tusks or bones that have been colored blue by iron phosphate or rarely green by copper. This type is discussed fully elsewhere in the course.
Ivory from the hippopotamus is denser than that from elephant and has a closer grain. The tusks are hollow and little solid material is available; consequently, it is used only for small work. It is, however, of a purer white, is not liable to split, and has a texture that may be thought of as between ivory proper and pearl shell.
This type is from the long tusks that hand perpendicularly from the upper jaw of the sea cow, troops of which exist along the icy coasts of the northern seas. The color is usually a yellowish cream. It was used in Oriental nations especially by the Persians, for sword grips. The Scandinavians have used it frequently for chessmen and caskets.
- Narwhal or "Unicorn"
Ivory from this small Arctic whale is seldom worked, usually being kept as a curio. The tusk is found only in the male, and usually there is only a single tooth for defense on the left side. Rarely, however, there are two, in which case they are twisted or entwined. The material possesses a beautiful spiral structure and a central cavity that extends to the end of the tooth.
- Wart Hog
Ivory from this boar is occasionally used for small objects. It is restricted to the canine teeth of the wold African swine and normally grows perpendicular to the upper jaw, sometimes attaining a length of twelve inches. The lower tusks, however, are never longer than six inches.
Elephant, hippopotamus and walrus ivory have a greasy to dull luster, a fair degree of toughness, no cleavage, a splintery fracture, a hardness of 2 1/2 to 2 3/4, and a violet-blue fluorescence. Acids cause no discoloration, but the application of heat results in shrinkage. The S.G. of elephant ivory varies from 1.70 to 1.85 and its R.I. averages 1.535. Hippopotamus ivory has an S.G. range of 1.80 to 1.95 and an R.I. of 1.545. Walrus ivory is slightly higher in both properties; i.e. a 1.90 to 2.00 S.G. and a 1.55 to 1.57 R.I. Ivory from the narwhal and wart hog have essentially the same properties as that from the walrus, except that the hardness is 2 3/4, 2 1/2 and 2 3/4, respectively, and the wart-hog type shows an even stronger violet-blue fluorescence.
Elephant ivory is characterized by an "engine turned" effect that is
visible on any cross-sectioned surface of a tusk (Figure 1); this
appearance is the result of a peculiar spiral structure that is found in
no other kind of ivory. Grain lines may also be visible, which are
straight in a longitudinal section (Figure 2) and curved in a large
cross section. Figures 1 and 2 were taken under 15x and 25x
respectively. In addition, wavy canals may be seen under 25x to 50x that
intersect the grain lines in the cross-section view (Figure 3). Both the
they serve only to distinguish between ivory in general and ivory substitutes.
Hippopotamus ivory is characterized by undulations similar to those of elephant ivory, but they are of perceptibly shorter wavelength.
Undulations are also visible in walrus ivory, but they appear
rather flattened; that is, the amplitude of the waves is less and the
tubes are larger in diameter and show a more obvious degree of
cross section is invairably characterised by a core of secondary dentine that is conspicuously coarser in texture.
Although bone has no relation to ivory, the two materials are similar in appearance. Bone is classified according to two main types: compact and cancellous. The latter is spongy in structure and is not suitable for decorative purposes. The compact type, which comprises the outer surface of all bones and the shafts of long bones t is sufficiently dense to resemble ivory. It consists of numerous cir¬cular units called "haversian systems." The center of each of these