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Ivory

Ivory is a hard, white, opaque substance that is the bulk of the teeth and tusks of animals such as the elephant, hippopotamus, walrus, mammoth, etc. Prior to the introduction of plastics, it was used for billiard balls, piano keys, buttons and ornamental items. The word "ivory" was traditionally applied to the tusks of elephants. Plastics have been viewed by piano purists as an inferior ivory substitute on piano keys, although other recently developed materials more closely resemble the feel of real ivory.

Structure

The chemical structure of the teeth and tusks of mammals is the same regardless of the species of origin, and the trade in certain teeth and tusks other than elephant is well established and widespread. Therefore, "ivory" can correctly be used to describe any mammalian teeth or tusks of commercial interest which is large enough to be carved or scrimshawed

Teeth and tusks

Pacific Walrus at Cape Peirce, teeth and tusks have the same origins. Teeth are specialized structures adapted for food mastication
. Tusks, which are extremely large teeth projecting beyond the lips, have evolved from teeth and give certain species an evolutionary advantage. The teeth of most mammals consists of a root and the tusk proper.
Teeth and tusks have the same physical structures: pulp cavity, dentine, cementum and enamel
. The innermost area is the pulp cavity. The pulp cavity is an empty space within the tooth that conforms to the shape of the pulp. Odontoblasts line the pulp cavity and are responsible for the production of dentine. Dentine, which is the main component of carved ivory objects, forms a layer of consistent thickness around the pulp cavity and comprises the bulk of the tooth and tusk. Dentine is a mineralized connective tissue with an organic matrix of collagenous proteins. The inorganic component of dentine consists of dahllite. Dentine contains a microscopic structure called dentinal tubules which are micro-canals that radiate outward through the dentine from the pulp cavity to the exterior cementum border. These canals have different configurations in different ivories and their diameter ranges between 0.8 and 2.2 micrometres. Their length is dictated by the radius of the tusk. The three dimensional configuration of the dentinal tubules is under genetic control and is therefore a characteristic unique to the order.Tooth and tusk ivory can be carved into an almost infinite variety of shapes and objects. A small example of carved ivory objects are small statuary, netsukes, jewelry, flatware handles, furniture inlays, and piano keys. Additionally, warthog tusks, and teeth from sperm whales, orcas
 and hippos can also be scrimshawed or superficially carved, thus retaining their morphologically recognizable shapes

Availablity

From the ancient times, ivory has been regarded as one of the most prestigious materials for carving. Due to the rapid decline in the populations of the animals that produce it, the importation and sale of ivory in many countries is banned or severely restricted. Much of the decline in population is due to poachers during and before the 1980s. Since the worldwide ivory trade ban in 1989 there have been ups and downs in elephant populations, and ivory trade as bans have been placed and lifted. Many African countries including Zimbabwe and South Africa claim that ivory trade is necessary both to stimulate their economies and reduce elephant populations which are allegedly harming the environment. In 2002 the United Nations partially lifted the ban on ivory trade, allowing a few countries to export certain amounts of ivory. Yet, a 1999 study done by Oxford University found that less than one percent of the five-hundred million US dollars ivory sales generate ever reach Africans; most of it goes to middlemen and vendors, so the effectiveness of the policy is in question. Kenya, which saw its elephant populations plummet in the decade preceding the 1989 ban, claims that legalizing ivory trade anywhere in Africa will endanger elephants everywhere in Africa as poachers would attempt to launder their illegal ivory with legal stockpiles. Trade in the ivory from the tusks of dead mammoths has occurred for 300 years and continues to be legal. Mammoth ivory is used today to make handcrafted knives and similar implements. A species of hard nut is gaining popularity as a replacement for ivory, although its size limits its usability. It is sometimes called vegetable ivory, or tagua, and is the seed endosperm of the ivory nut palm commonly found in coastal rainforests of Ecuador and Peru.
What Is Ivory?

Ivory is the teeth of animals. "True" ivory comes from elephants and mammoth; however, the term is generally applied to the tusks of other mammals, and some synthetics. Chemically, ivory is similar to bone and antler, and comprises a collagen matrix with a mineral component. Unlike bone, ivory has no blood vessel system, and is therefore more dense.
The most commonly found ivories in North America come from elephant, walrus, sperm whale, and hornbill. It is possible to tell these ivories apart, as they are structurally different.

Elephant Ivory

This category includes ivory from both Indian and African elephants, as well as ivory from mammoths and mastodon. The tusks, or upper incisors, of these animals are used. They can have a cross section of up to 20cm (8"), and be up to 2.5m (almost 3 yards) long. They are oval in cross section, and are made up of a hard, dense tissue called dentin, which is made up of 70% inorganic material, and 30% collagen. Unlike human teeth, elephant tusks do not have an enamel coating. They do have a cementum layer, however; ivory dealers refer to this as the "bark" or the "rind". Occasionally this layer is retained on a piece of worked ivory. One-third to one-half of an elephant tusk is hollow.
Growth occurs as layer upon layer of calcified tissue is deposited on the interior of the tusk; you can see these concentric oval growth lines (called the Lines of Owen) in cross section. If you cut ivory lengthwise, these lines appear triangular. Fine and even near the hollow of the tusk (the pulp cavity), these lines become wavy and have milky areas between them as you get closer to the outside of the tusk.

Unique to elephant ivory are the Lines of Retzius. These fine intersecting lines are visible in cross section, and give an engine-turned effect (intersecting lines with a diamond shape between them).
Generally, elephant ivory has a fine, even grain and is easily carved in all directions. It can be thinly cut (i.e. for piano keys), and can be more deltcately carved than bone. This ivory is often painted or stained, dyed, and gilded. When cut, the pores of the ivory fill with an oily substance, which helps the ivory polish up nicely.

Hippopotamus Ivory

This is the second most commonly used ivory, after elephant ivory. Often used for flat items, such as buttons and inlays, it comes from the lower canines and incisors of hippos. The size varies, depending on the size of the animal.

The lower canine is curved, and has a triangular cross section; the incisor is straighter, and has a circular cross section. Both have two layers of dentin: an outer, primary dentin, and an inner, secondary dentin. The innermost layer has a marbled appearance which differs by species, and can even appear to have a greenish cast. The pulp cavities of these teeth are fairly small. Unlike elephant ivory, hippo ivory does have a thick enamel coating.

Hippo ivory is denser than elephant ivory, harder to carve, and has a finer grain. There is none of the "engine turned" effect in cross section, rather, hippo ivory has concentric rings in cross section. Finally, hippo ivory is less prone to decay than elephant ivory.

Walrus Ivory

This ivory comes from the upper canines of walrus. It is oval in cross section, and can be over 2 feet in length. It has an inner dentin layer (which has a high mineral content; it forms as the tusk grows, and leaves a marbled look on finished objects), an outer dentin layer, and a smooth, dense cementum layer. Walrus ivory is used primarily for small objects.

Sperm Whale Ivory

Thirty teeth of the sperm whale can be used for ivory. Each of these teeth, up to 8" long and 3" across, are hollow for the first half of their length. Sperm whale ivory is easily confused with walrus ivory, as both have two distinct layers. The inner layer of sperm whale ivory, however, is much larger. As well, in a longitudinal section, sperm whale dentin has yellow "globules" included in the marbilization.

Hornbill Ivory

This comes from the casque or epithema of the Helmeted Hornbill, a bird native to the East Indies. It is distinguished from the rest of its family (the Bucerotidae) by having the front of its almost vertical and slightly convex epithema made of a solid mass of horn. This "horn" or "ivory" is quite hard and closely-textured. This substance is used to make small objects such as buckles and brooches, and is highly valued by the Chinese. In cross section, you can see a bright yellow interior with a scarlet rim.

Vegetable Ivory

The source of vegetable ivory is the inner seed of the South American ivory palm, and is thus completely made of cellulose (rather than collagen). These seeds are the size and shape of a small hen's egg, are very hard, and are solid all the way through. Vegetable ivory is smooth, takes a good polish, easily absorbs dyes, and is relatively inexpensive. It is used for small items only, such as dice and buttons. Since about WWII, vegetable ivory has been largely replaced by plastics.

Synthetic Ivories

Since 1865, when it was first invented by Alexander Parkes, celluloid has been used as an excellent ivory substitute. Casein has also been used. Names for these "faux ivories" include French Ivory, Ivoride, Genuine French Ivory, Ivorine, etc. Both grain patterns and the engine turned effect are added -- in general, the patterns of these are very regular in the fakes, and more irregular in the real thing. In instances of very good imitations (i.e. using celluloid), chemical tests are required to tell real ivory and the fakes apart.

     Ivory is used in organbuilding primarily for key coverings and drawknob heads.

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