A background to tortoiseshell

A BACKGROUND TO TORTOISESHELL

NOTE: Tortoiseshell derives from three endangered species of marine turtles. It is, however, the view of Organic Gems that in order to help protect and save these animals, it is necessary to know what tortoiseshell is, and how to recognise it. The following is therefore not in any way intended as condoning the use of modern tortoiseshell, or the poaching of animals, but purely to educate

Female hawksbill turtle returning to the sea after laying eggs.

Tortoiseshell is derived from the shell of marine turtles. Their bodies are encased in a bony shell (the ‘carapace’ on the back, and the ‘plastron’ on the stomach), which are covered by a leathery skin, which in turn is covered in horny plates or ‘scutes’. When worked, these are called ‘tortoiseshell’. Their flippers and the sides of their bodies are covered in skin which can be tanned to make leather. Unlike tortoises, they cannot retract their heads into their shells.

The most common tortoiseshell comes from the hawksbill turtle (Eretmochelys imbicata) because – unlike other turtles -- the scutes on the hawksbill’s carapace (back) are not completely welded to the skin underneath, but overlap like tiles on a roof, allowing them to grow in thickness during the turtle’s life, as well as in size. The hawksbill has thirteen main scutes on the carapace, plus twenty-five marginal scutes – those around the edge of the shell. On the plastron there are thirteen large, eight infra-marginal, and many smaller axillary scutes. The hawksbill gets its name from the slightly beak-like shape of its mouth. A fully-grown hawksbill’s scutes can reach a thickness of up to almost one centimetre.

Left, hawksbill turtle carapace, with overlapping scutes. Right, plastron scutes which do not overlap.

(The young turtle was in the process of being tagged.)

In theory, scutes from any of the order of animal called Testudines (which includes tortoises and terrapins as well as marine turtles) can be used but in practice it is less successful, however tortoiseshell from both the green turtle (Chelonia mydas), which has a fan-like pattern on the carapace, and the loggerhead turtle (Caretta caretta), have been used. They are less thick than those of the hawksbill, so have been used mostly for veneer.

Tortoiseshell is made of a hard, insoluble protein called keratin, which contains large amounts of sulphur-rich amino acids and is common in animals as it is the prime constituent in hair, horn, hoof, nails, claws, quills, and is also present in skin. It is a thermoplastic material, that is to say it can be heated, moulded and retain its shape when cooled, and the process can be repeated. When heated sufficiently, it softens and becomes sticky. Tortoiseshell scutes can be welded so that several layers can ‘glue’ together when heated and pressed, giving a thicker material with which to work. It can also be sliced thinly and pieces welded end-to-end with a small overlap, to give larger sheets of material.

The scutes on the plastron have virtually no mottling, but are a pale honey colour, giving the so-called ‘blond’ tortoiseshell. They do not overlap in any of the turtles but are welded to the skin underneath which means that they are thin. It was therefore common practice to weld these together.

Left, tortoiseshell from the carapace and right, 'blond tortoiseshell' from the plastron. See photos above.

Due to its thickness, tortoiseshell from the hawksbill has been used to fashion many and varied objects. Being thermoplastic meant that it was an ideal base for piqué work -- a delicate form of decoration involving pressing slivers of metal (usually silver) into the heated, softened and slightly sticky material. Tortoiseshell was seldom dyed, but sometimes backed so that the colour of the backing showed through the pale areas of the material.

Dressing table jar with tortoiseshell lid.

HOW TO RECOGNISE TORTOISESHELL

Tortoiseshell is known for the distinctive mottled pattern of the carapace scutes. Under magnification this pattern can be seen to be made up of patches of tiny blurred spots of colour. As it has always been expensive, copies have been made in cheaper materials, but none of them have succeeded in truly copying the mottled pattern.

Horn is very closely related to tortoiseshell because it has so many of the same properties, but it is far more readily available. Although it may be patterned, none of it has the same mottling as tortoiseshell, and so it has been painted as an imitation. However painted mottling is always on the surface, while the mottling in tortoiseshell penetrates the material. This can be observed by careful examination under magnification.

Less convincing than horn but far more common are fakes made from various plastics. These have been on the market since the middle of the nineteenth century when semi-synthetic plastics such as cellulose nitrate were used as imitations. Today tortoiseshell is still being copied in modern plastics and used for a variety of purposes from hair ornaments and spectacle frames to laminates.

The mottled pattern in plastic imitations is caused by the addition of colour to a clear base. The result is usually that the colour appears in swirls or distinct patches. Again, careful examination – possibly under magnification – will show no indication of the blurred spots of real tortoiseshell.

Left: mottled pattern of tortoiseshell, and right: swirls of colour in plastic imitation.

Both shown under magnification.

It is slightly more problematic to recognise blond tortoiseshell, which can look very like dark honey-coloured plastic. The quality of workmanship involved in producing the item may give some indication, and any area of damage on tortoiseshell may show some flaking of the layers of keratin of which it is made. Moulded plastic does not flake. Very feint striations may also be visible in tortoiseshell but are absent in plastic.

The material in its raw state is dull and displays a snaking, circular pattern of growth rings, which are polished off when the material is worked, giving the surface a high lustre. With time the lustre becomes dull and traces of the circular patterning reappear, giving a moiré silk effect. No other material displays this. Re-polishing with appropriate abrasives renews the lustre, but inevitably removes a little of the material. This should only be done by specialists.

TESTS

Visual examination using magnification (a 10x lens) should be sufficient to tell whether an item is made of tortoiseshell or is an imitation.

In items that are thin enough to be partially transparent or translucent, and not too large, it may be possible to examine them on a polariscope (an instrument frequently used by gemmologists), where crossed polars will show a rainbow of colours in tortoiseshell, but, at best, a few swirls of colour in plastic which otherwise remains dark. This can be a useful test for blond tortoiseshell.

Left, 'blond tortoiseshell' under crossed polars (magnified), and right, the moiré silk effect of old tortoiseshell

which has lost its polish.

The hot point test (touching the surface with a red-hot tip of a pin), is destructive as it will always leave a mark, and should only be undertaken by an expert and as a last resort. Further, it can be dangerous as the early plastic, cellulose nitrate, is highly combustible. Melted plastic gives off a different smell to tortoiseshell, but horn will smell the same. (See 'Early Plastics as Imitations of Organics'.)

TRADE BANS AND THE PLIGHT OF THE TURTLES

The marine turtle has been hunted for centuries. Local people valued the meat, eggs, and leather (from the skin on the necks and flippers). In the West, turtle soup was a delicacy (the best came from the green turtle, so called because the animal’s fat has a green tinge), and in the days before refrigeration turtles were caught and kept alive – sometimes for weeks -- on sailing ships to provide fresh meat for the sailors.

But the beautiful shell proved irresistible, and hawksbill turtles were at one time being killed in their hundreds of thousands annually to provide this fascinating and versatile material. At first it was believed that the scutes on a turtle would grow again if removed or shed, and the animals were held over fires until the scutes melted sufficiently to become loose. The hapless creatures were then returned to the sea where they died.

Today marine turtles are covered by bans or hunting moratoria in most countries. They are all listed under CITES Appendix I, which forbids all international trade in any part of the animals. Currently 183 countries are signatories of CITES (the Convention on International Trade in Endangered Species of Flora and Fauna). Even with these bans, the odds are stacked against the severely endangered turtles. They spend their entire lives at sea, with the exception of the females’ brief visits of about an hour’s duration for laying eggs and burying them in the sand on the sea shore. The males never return to land.

The female hawksbill turtle reaches maturity at the age of twenty to thirty years. She then measures about one metre in length and weighs almost one hundred kilograms (one kilo of which is tortoiseshell) After that, every couple of years she has an egg-laying cycle during which she lays about six hundred eggs, in batches of about one hundred at a time. Amazingly, she returns to her own natal beach to lay the eggs. After six weeks the hatchlings emerge from the sand at night and find their way to the sea, following the light on the horizon.

Hatchlings collected from a hotel lobby, and waiting to be safely released in the sea.

The small hatchlings are about two inches in length, and anything with a mouth or beak larger than two inches can eat them. Mankind is also largely to blame for the high mortality rate of the hatchlings. Tourism has caused many of the beaches to be built upon, so the returning females have only a narrow strip of beach for their nests instead of wide, unspoilt beaches. Further, the beaches are tourist playgrounds and are often illuminated by lights from hotels. Disorientated by the light, the hatchlings frequently head inland instead of out to sea when they hatch. It is estimated that at most only one in every thousand hatchlings born reaches maturity.

Man’s love of tortoiseshell continues, and some efforts have been made to farm turtles. So far only greens have bred successfully in captivity, but the scutes of these captive turtles are of inferior quality and cannot easily be moulded or welded. Plastic imitations have never attained the right look or feel.

There are still places around the world where tortoiseshell items, and indeed whole stuffed turtles, are openly for sale, but it is illegal to import them to most countries, including the United States, Australia, and the whole of Europe. The domestic sale of tortoiseshell is also heavily regulated in most countries. New material should never be purchased, and it is advisable to check on the law if trading in old items, either domestically or internationally.