Tortoiseshell

Tortoiseshell (also Bissa, tortoiseshell, of nordd. / Dutch. Schildpadde for turtle ) is a biogenic material from the flat horny scales ( Scuta ) of the dorsal shield ( carapace ) can be obtained from three species of sea turtles.

Origin

The drawing and the quality tortoiseshell depend on the turtle and the geographical origin of the animals. Light yellow tortoiseshell with a brown to black drawing comes, for example, mainly from the East Indies. Bright red-brown tortoiseshell with a dark red-brown drawing on the other hand comes from the Egyptian tortoise. American tortoiseshell is usually red and blotchy. Monochromatic light plates ( blind tortoiseshell) are a rare specialty.

The carapace of the hunted for their meat soup turtle ( Chelonia mydas) was due to their small thickness used for the production of lanterns. The loggerhead sea turtle (Caretta caretta) and hawksbill ( Eretmochelys imbricata ), however, have horny plates that are clear translucent and colorful colored ( yellow, red, brown, black) or flamed gewölkt. Therefore, they were only caught because of their tortoiseshell.

Tortoiseshell (ba SIG4 ) was already imported under the kings of Larsa from the Persian Gulf. The letter UET V 678 from Ur mentioned 30 pieces ba SIG4. Even the ancient Egyptians used tortoiseshell, tortoiseshell objects were also found in Nubian graves.

In the 18th and 19th century tortoiseshell was imported mainly from the Bahamas, the West Indies, the Cape Verde Islands and from Guyana to Europe. The Dutch trading company imported tortoiseshell from the West Indies and the Moluccas and Spain most of the Malabarinseln. Other occurrences were found at the time in Madagascar, China, New Guinea and the Bismarck Archipelago.

The tortoise was not won in the regions of origin and shipped to Europe. This shiploads were destroyed by worm infestation, as this has been greatly favored by the long transport distances and lack of air supply or circulation. In European ports - such as Marseille, Amsterdam and Hamburg - the tortoiseshell was then sold by the pound to dealers and artisans.

In 1784 the cost of a pound of tortoiseshell in Amsterdam 6 to 15 guilders. 1895 were sold with a value of 350,000 marks in Hamburg 9305 kg tortoiseshell.

Extraction

From the turtle shell was used only the back plate, which consists of twelve to a hexagonal medium flap arranged panels. In order to solve the coveted material of the heat needed tortoise shells. Writings from the 16th to the 20th century can be seen that to the surviving animals were placed in boiling water or held over a fire. The tortoiseshell softened under the influence of heat and this could be replaced with a knife of tanks.

In the 18th century the flesh of turtles was considered unpalatable. Since the European hunters also believed that the tortoise would grow, the animal was when it survived the peeling procedure released. In fact, to be found in Grzimek's animal life that could approximately reproduce again at very young animals of the tank.

Obtained from a 75 -pound turtle a viable tortoiseshell yield of about 2.5 kg.

Processing and use

The tortoiseshell is very similar to the horn and how this is largely of keratin.

The thermal properties of tortoiseshell make this processing would not be possible. Is it cold or hard and brittle ( the Mohs hardness is about 2.5 ), so it is elastic and pliable by heating. However, if it exposed to extreme heat, it might lose its transparency.

A typical processing operation is first aimed at leveling the shield plates. The plates are thereby heated in boiling water until they deform under its own weight. After softening the plates are pressed, but may not cool down too fast thereby. For this reason bags were used with hot sand or preheated metal plate for the pressing operation. Then allowed to cool down the plates under pressure. The prepared plates must be equalized, ie brought to a uniform thickness, are. Thus, the transparency of the tortoiseshell can be worked out.

If larger pieces of tortoiseshell required, individual plates using a combination of heat and pressure can be welded together.

With the help of heated metal molds which can also pre- heated tortoiseshell be brought into different shapes. After it has cooled in the molds, it retains its new shape.

After processing, tortoiseshell, the individual pieces are glued to a backing of wood. Frequently, the transparency of the material is utilized and the tortoiseshell colored paper background. This had, in addition to the reinforcement of the color impression, the advantage that the wood grain showing through, and to recognize the pattern of the tortoiseshell.

Threat to sea turtles and conservation

The hunting of sea turtles because of their tortoiseshell was responsible alongside the drowning of many animals as by-catch in fishing nets and the destruction of habitat by obstruction of coastal sections relevant for the stock collapse in some turtle species. Through the Washington Convention of 1973 ( ratified by the Federal Republic in 1976 ) the species concerned were therefore placed under strict protection and prohibited trade with tortoiseshell. Nevertheless, article find tortoiseshell continue in some tourist regions as souvenirs. Imports to Germany is prohibited and punishable.

Another form of conservation is the use of substitutes. Imitations of tortoiseshell were once, shortly after it came into fashion, prepared by brings on white horn, bone and ivory even by pickling similar colors and drawings. [ 1 comments ]

As the celluloid was developed, it was used both as a substitute for ivory and for tortoiseshell. Later, the celluloid was as superseded by the newer DPN and finally by modern plastics such as the Rodoit.