Tortoiseshell

Tortoiseshell is the name given to the mottled, golden or reddish and brown, translucent, homy plates or scutes covering the shells of certain species of marine turtle. The best known and by far the finest tortoiseshell comes from the hawksbill turtle, but the scutes of the green and the loggerhead turtles have also been put to some decorative uses. 

Although marine turtles are constantly being researched, our knowledge of them is somewhat limited as, from within minutes of hatching, they live their entire lives in the sea. Only the females come ashore to lay their eggs, after which they return quickly to the sea (Fig. 8.1). It 

A marine turtle can lay up to 800 e gs in one season, in batches of 90 to 150. The e hatch about nine weeks after they hove been laid. The baby turtles (the hatchlings) emerge at night and make their way strai i into the sea, attracted by the celestial li t shinir on the surface of the water. 

In the sea, turtles can stay under water for a short period of time, but must surface regularly to breath. 

Tortoiseshell is made of keratin, the same material as, amoi other thii, horn. The colour in tortoiseshell comes om the pigment melanin, deposited in minute globules of about 100 micron in diameter. Like keratin, melanin is very common in the animal kingdom as it is also the pigment vrtiich gives, for example, feathers, skin, and octopus ink their colour. 

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Torsional Braid Analyzf Torsional pendulum Tortoiseshell Torulaspora rosei Torula yeast... 

Heat is used to darken amber, ivory, and jade to simulate age. Pieces of amber and tortoiseshell can be reconstmcted, ie, joined under heat and moderate pressure. By careful heating in oil, milky amber can be clarified when the gas and water within small bubbles diffuse out of the stone. If heating is rapid, the attractive sun-spangle cracking shown in Figure 1 results. 

Because of its lipophilicity and refractory character, the toxic effects of dieldrin may be carried throngh to the next generation. In one example, dosing of female small tortoiseshell bntterhies (Aglais urticae) with dieldrin led to an increased number of deformed adults emerging from pupae (Moriarty 1968). 

Jazzy, marbled, or tortoiseshell effects can be produced in moulded components by using starting materials in a selection of different colours, or by using two or more masterbatches. Such effects are attractive for certain purposes but it is important to remember that when preparing the melt intensive mixing must not take place machines are made specially to ensure that the pattern required in a moulding can be reproduced precisely. 

These hair ornament are made of plastic, as imitations of tortoiseshell. 

Ivory can be inlaid with materials such as mother-of-pearl, coral, tortoiseshell or ebony. This has been popular in Japan, where it is called Shibayama wodc. 

Japan was strongly influenced by China, and their craftsmanship is almost on a par with that of the Chinese. Originally, ivory was used as inlay, sometimes together with tortoiseshell, silver and gold. And, like the Chinese, the Japanese later developed the an of carving it. 

Netsuke - toggles worn on the clothit gre probably the best known Japanese carved items. Also made were pres, seals, and boxes. Later many of the items produced were made specifically for export to the west (Fig, 3.18). As in India, ivory in Japan has also been used as a background and inlaid with other precious nutterials such as coral and tortoiseshell. They called the style Shibayama, after the man who was a master of the craft. 

In past times horn could be peeled into thin layers to use, for example, as a veneer in place of tortoiseshell. This is not done today as modem horn does not peel so easily. 

Horn can be inlaid with silver pique work or with mother-of-pearl. As with tortoiseshell, this is done imder heat and pressiure, and the material to be inlaid is pressed into place. It is not necessary to carve out a hollow for the inlay. Theoretically, it should not be necessary to use glue as the material will contract to hold the inlay as it cools, but in practice, glue is often used. 

Horn can be bleached and painted, as, for example, when imitating tortoiseshell. This was sold as mockshell in the nineteenth oentuiy and was used mostly for hair ornaments, fons and combs. Hom does not last finever, but deteriorates with age. For this reason there are few very old items to be found in museums. Damp, heated storage is especially damaging to hom. 

There have been few real simulants of horn as supply is plentiful and the material is relatively inexpensive. However, it is not cheap to work as it must be hand crafted, so today it is regarded as a luxury item. Horn has itself been used as a simulant of other materials, most notably tortoiseshell, black coral and jet. 

Patches of minute blobs of brown colour, together with a lack of striations, indicate that the material may be tortoiseshell (Fig. 8.15). 

Surhice detetiotation is not a reliable indication of the nature of the material as both plastic and horn dull with age and both scratch easily. Fiqu6 work, good workmanship, or a good finish would all be indicators that an item is made from horn or tortoiseshell, rather than plastic. 

Ultraviolet l iit. Viewed under UV light both horn and tortoiseshell show a slight fluorescence. This is more noticeable in the paler areas of the two materials. 

Sectility. This is not a useftil test as horn, like tortoiseshell and plastic, can be paired with a sharp knife. 

Horn jewellery is, as a rule, thicker and less delicate than jewellery made of tortoiseshell, though it can be difBcult to tell them apart. A notable exception is the art nouveau jewellery, made at the turn of the twentieth century. Somewhat surprisingly, hom was used more than tortoiseshell, and was bleached, carved, and combined with enamel, gold, ivory, pearls and precious stones to produce magnificent pieces of extraordinary beauty. Masters of this art included Mme Bont6 (Fig. 7.13) and George Pierre, and of course the ultimate master, Ren6 Lalique. 

Blond tortoiseshell comes fi-om the scutes on the belly of the turde, which are a pale honey colour and almost transparent. They are thin, and several must be welded together in layers for the material to be thick enough to work. 

Tortoiseshell is a thermoplastic, that is to say it can be softened by heating, and then shaped or moulded, retaining the new shape when cooled. The process can be repeated. 

The hawksbill turtles, Eretmochelys imbracata, grow the best tortoiseshell. They get their name from the narrow, hooked, beak-like appearance of their mouths. They live aroimd coral reefs but can travel long distances, as has been proved by turtles that have been tagged and tracked using satellite transmitters. Hawksbills are fotmd worldwide in tropical and subtropical waters, and they feed primarily on sponges. 

Tortoiseshell derived from the hawksbill is very versatile and can be used in numerous ways, unlike that of the other turtle species, where it is much thinner and so has very limited use. 

The scutes on the carapace of the loggerhead are not nearly as pretty as those of the other turtles, and are as thin and fragile as those of the green turtle. Nonetheless the material has been used as tortoiseshell, thou mainly as veneer. The shells are also sold whole. 

Figure S.5 Three tortoiseshell boxes left, on vhite basej bottom, blond tight, natural.

Figure 8.7 Tortoiseshell card cases left, pressed rights carved.

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