Ivory

Ivory is dentine — the material that makes up the bulk of a tooth beneath the enamel — from a tooth large enough to carve. Elephant and mammoth tusks are the main source; walrus, hippopotamus, sperm whale and narwhal teeth all give ivory with distinct characters.

By composition it is roughly 70% mineral and 30% organic: carbonated hydroxyapatite crystals in a collagen matrix, which is the same recipe as bone. What separates it from bone is the arrangement. Bone is a porous structure with a blood supply, riddled with Haversian canals. Dentine is dense and near-solid, penetrated only by microscopic tubules radiating from the pulp cavity.

That density is the whole of its value as a material. Ivory can be carved across the grain as readily as along it, holds an edge of detail that wood will not, takes a polish that looks wet, and is slightly elastic rather than brittle. Nothing natural does all of that, which is why it survived as a working material for so long after it had become indefensible to obtain.

The definitive test is visible with a hand lens and takes a moment: Schreger lines, the cross-hatched pattern seen on a transverse section of elephant or mammoth ivory, formed by the interference of the tubule bundles. They appear in no other ivory and in nothing else at all.

The angle where they intersect near the outside of the tusk separates the two species that matter legally. In mammoth it is characteristically acute — below about 90 degrees — and in elephant obtuse, above about 115. That single measurement is the working basis of enforcement, because mammoth ivory is legal to trade and elephant ivory is not, and the two are otherwise nearly indistinguishable.

Against bone, the test is the opposite one: bone shows Haversian canals as fine dark pits and streaks under magnification, and ivory shows none. A hot needle distinguishes both from plastic, which melts and smells; ivory and bone char and smell of burning hair.

Vegetable ivory — the endosperm of the tagua palm nut — is convincing, is a genuine substitute rather than a fake, and is given away by its size, by a small central cavity, and by turning pink under sulfuric acid.

Ivory carving is Palaeolithic. The Löwenmensch of Hohlenstein-Stadel is mammoth ivory around forty thousand years old and is among the oldest figurative sculpture known, which puts ivory alongside stone as one of the first materials worked for something other than use.

Its industrial phase was brief and enormous. Piano keys, billiard balls, cutlery handles, combs and piano-key-white everything consumed tusks at a rate that nineteenth-century writers already described as unsustainable, and the search for a substitute produced one of the founding events of the plastics industry: John Wesley Hyatt's celluloid, patented in 1869, was developed explicitly as a billiard-ball ivory replacement.

So the material that plastics were invented to replace is also the material whose replacement began the polymer age — a connection worth making whenever plastic is discussed as an unambiguous mistake.

African elephant populations fell from something on the order of a million in 1980 to around 600,000 by 1989, almost entirely to ivory poaching. CITES banned international commercial trade in African elephant ivory in 1989, effective 1990, and the price collapsed and the killing fell sharply.

What followed is genuinely contested, and it would be dishonest to pretend otherwise. Two sanctioned one-off sales of stockpiled ivory, in 1999 and 2008, were argued for as a way to fund conservation from existing stock; several analyses associate the 2008 sale with a subsequent rise in poaching, on the theory that any legal supply gives cover to laundering, while others dispute the causal link. Southern African states with growing elephant populations argue that a controlled legal trade would fund the communities bearing the cost of living with elephants, and their case is not frivolous.

What is not contested: the enforcement problem is legal supply of any kind, because a legal category is a channel. That is why the recent direction of travel — domestic market closures in China in 2017, the United States, the United Kingdom's near-total ban in 2018 — has been towards eliminating the channels rather than regulating them.

Mammoth ivory sits in the gap, legal because the animal is extinct, and has grown into a substantial Siberian trade with its own permafrost-damage problems and its own role in disguising elephant material.