Tortoiseshell E-Book

Maggie Campbell Pedersen

• Herausgeber: NAG
• Kategorie: Lebensstil
• Sprache: Englisch

Seitenzahl: 221

Veröffentlichungsjahr: 2021

Beschreibung

Tortoiseshell, derived from marine turtles, has been used in decorative work for thousands of years. It featured in trade with, amongst others, the Babylonians and the Romans. In Europe it was used for furniture veneer in the seventeenth century, while in Polynesia it was used for personal adornment although turtles were viewed as sacred. Today it is important to be able to recognise tortoiseshell as all marine turtles are protected species and subject to global trade bans. This book covers the historical use of tortoiseshell in various parts of the world; how tortoiseshell artefacts were made, from moulding to pique work; turtles species, their habitats, and their conservation status today; the identification of tortoiseshell, and how to distinguish it from imitations, notably horn or the early plastics such as celluloid; testing methods , both simple and advanced and finally, information on laws and regulatory bodies. This is the only book that covers tortoiseshell from all aspects.

Leseprobe

TORTOISESHELL

TORTOISESHELL

Maggie Campbell Pedersen

First published in 2021 by NAG Press,an imprint of The Crowood Press Ltd,Ramsbury, MarlboroughWiltshire SN8 2HR

[email protected]

www.crowood.com

This e-book first published in 2021

© Maggie Campbell Pedersen 2021

All rights reserved. This e-book is copyright material and must not be copied, reproduced, transferred, distributed, leased, licensed or publicly performed or used in any way except as specifically permitted in writing by the publishers, as allowed under the terms and conditions under which it was purchased or as strictly permitted by applicable copyright law. Any unauthorised distribution or use of this text may be a direct infringement of the author’s and publisher’s rights, and those responsible may be liable in law accordingly.

British Library Cataloguing-in-Publication DataA catalogue record for this book is available from the British Library.

ISBN 978 0 7198 3145 4

The right of Maggie Campbell Pedersen to be identified as author of this work has been asserted by her in accordance with the Copyright, Designs and Patents Act 1988.

Photo creditsAll photos by the author, © Maggie Campbell Pedersen, unless otherwise stated.All illustrated items are in private collections unless otherwise stated.

Contents

Foreword

Dedication

Introduction

Acknowledgements

1  Turtle Species

2  Conservation and the Dangers Faced by Turtles Today

3  What is Tortoiseshell?

4  Identifying Tortoiseshell and its Simulants

5  Testing Tortoiseshell

6  Treatments and Care

7  History

8  Other Keratins Used in the Decorative Arts

Appendix I Laws and Regulatory Bodies

Appendix II Quick Reference Chart for Worked Materials

Glossary

Bibliography

Index

Foreword

From the moment my curiosity for gems and gemmology started, back in the 1980s, I always had a thing for those gem materials that were produced by living organisms, the then so-called organic gems (now also known as biogenic gems). It was in the capacity of an avid gem knowledge addict that I met Maggie Campbell Pedersen, the author of numerous articles on that subject at Gems & Jewellery magazine, published by Gem-A (The Gemmological Association of Great Britain). Her vast knowledge was made into a book in 2004, Gem and Ornamental Materials of Organic Origin, which I still use as a reliable source of information on organic gem materials and their imitations. I met Maggie back in 2008 and got to know her better after I was elected vice-president of the Coral Commission of CIBJO, The World Jewellery Confederation, as we shared a common passion for gemmology and education; we soon started sharing information on coral and other gem materials.

Being from Portugal, where ivory art was quite important in the sixteenth and seventeenth centuries, I found her 2015 book Ivory a tremendous aid for a better understanding of the material and the imitations, especially the post late-1800s ones. Due to the same curiosity for art history with strong cultural heritage I was very happy when she told me she was preparing a new book, this time on tortoiseshell: a gem material that has been rather neglected in the gemmological literature. A few months later, I received a lovely email from her challenging me to write the foreword to this brand new title, a challenge that I accepted with great joy as Maggie is, if I may say so affectionately, the ‘Organics Queen’.

The gem, jewellery and antiques’ ecosystem is greatly enriched with the release of this comprehensive educational book. Tortoiseshell – actually a misnomer – is derived from the marine turtle, now a protected species that faces serious conservation challenges and is currently protected under global conservation regulations. However, it was extensively used in the past and up to now there has been no major resource of information on this organic gem for gemmologists, museum curators, antique dealers or art historians. The author, also known for her photography skills, had included a chapter in her 2004 book dedicated to the natural polymer produced by a few marine turtles, most notably the hawksbill turtle, that is known as tortoiseshell. But apart from that, Maggie’s regular contributions to the Gems & Jewellery magazine, and the very few pages dedicated to this material in the traditional gemmological literature or in most gemmology course notes, it becomes clear that there is a need for a comprehensive and well-structured document on tortoiseshell. After many years of research, the author has added this book to the gemmological literature; it is an interesting and complete overview covering biology, history, nomenclature, biodiversity, conservation, treatments, imitations and, of course, gem identification.

As a gemmologist, I particularly enjoyed the chapters on identification, not only on the gemmological side with the explanations given on the classical gemmological techniques and the more complex and advanced laboratory methods, but also the distinguishing visual features that one should look for on an artefact to positively identify true tortoiseshell and separate it from the many lookalikes, such as horn, baleen and artificial products. The author cleverly organizes the section on artificial products in a chronological fashion, introducing the early imitations like celluloid from the late 1800s, as well as the early twentieth-century casein, and the modern plastics like acrylic, polyester or PVC.

One of the most interesting facts that we learn from this book is that tortoiseshell is a natural polymer, and therefore a ‘natural plastic’ – a term that is usually associated with artificial imitations of gems that are in fact better described as synthetic or semi-synthetic plastics. We should be much more careful when using the word ‘plastic’ in gemmology, as the term has a complex meaning.

The numerous applications of tortoiseshell, besides jewellery, receive good attention here. Many uses of the material are known in the decorative arts, namely in marquetry such as Boulle style, in Japanese Bekko work, in piqué work and in moulding scutes together as in Indo-Portuguese sixteenth/seventeenth-century small caskets. The use of this gem in ancient times is also discussed, although there are very few examples of the material in archaeological sites due to its lack of durability. The challenges in the manufacturing techniques of tortoiseshell also receive attention in this book, which is valuable information for those involved in the conservation of artefacts.

To conclude, this book is not only a great source to a gemmologist for the identification of tortoiseshell and its most common imitations, but also a relevant reference for decorative art historians, antique dealers, art conservators and collectors as an aid to the understanding of this extraordinary natural plastic produced by marine turtles.

Rui Galopim de Carvalho FGA DGAVice-President CIBJO, Section AFounder, Portugal Gemas Academy

Dedication

For my sister Alison, and in memory of my brother Neil.With my love.

Introduction

To see a hawksbill turtle emerge slowly from the sea is like witnessing something from a pre-historic world. To watch as she then drags her heavy body up the beach to a suitable spot to make a nest, proceeds to work at digging the nest, laying the eggs and then covering them and disguising the nest, fills one with awe. An hour and a half later, and surely exhausted, she drags herself back to the sea, leaving the eggs to incubate and then her babies to hatch about sixty days later. Just as awe-inspiring is to see the babies emerge from the nest and scramble down the beach as fast as their little flippers will carry them, and then see them tossed about in the waves at the water’s edge before they determinedly swim out to sea, apparently none the worse for the experience. Knowing the perils that await them in the sea is heartbreaking and one cannot be surprised that so few make it to adulthood.

Twenty years ago I spent two weeks patrolling beaches in Barbados at night, watching the nesting process, checking the nests, marking them, measuring and tagging turtles, and collecting hatchlings from hotel lobbies, the lights of which they had mistaken for the horizon. Sometimes I sat in the sand watching a nesting turtle inadvertently dig up another nest, the eggs flying out behind her as she swept the sand with her back flippers. Turtle eggs are not easy to catch, especially in the dark. We reburied them, but their chances of survival were minimal. At other times we had to dig up the whole nest and choose a better location for the eggs because the turtles did not always choose wisely.

Turtles are slow and they look ancient. They are not warm and cuddly. They show no emotions. Yet they are utterly fascinating. So too is the horny material that covers the shells of some of them, called tortoiseshell. It is very beautiful when worked, and the craftsmanship and skill required has to be admired.

In no way would I wish to harvest tortoiseshell from turtles today; however, in order to protect the animals it is necessary to know about them. In order to follow the various laws on trade in endangered species we need to recognize tortoiseshell when we come across it. Furthermore, tortoiseshell is very beautiful, it has a long history and it features in some exquisite items in the world of decorative arts.

Tortoiseshell has been admired and used for decorative purposes for thousands of years. Because of the nature of the material there are no very old examples still in existence – the oldest is unlikely to be more than 400 to 500 years old. It is, therefore, difficult to say with certainty exactly where and how it was used, so that must be deduced from early writings. Even then, it is not always clear, as the material might, for example, be mentioned in a list of trade goods, but with no mention made of the use to which it was put. Further, ‘turtle shell’ might refer to a whole carapace and not just the scutes, and often no differentiation was made between tortoises and turtles, or between marine turtles and freshwater turtles living in lakes and rivers. It is only when the description is more specific that it is possible to deduce that the material is the scutes of marine turtles; that is, what we today call tortoiseshell.

Turtles and tortoises have been the subject of myths and legends for many millennia, and have been regarded as symbols of steadfastness, longevity and even immortality. Their images can be found depicted in cultures wherever the animals might have been encountered, from Ancient Egyptian tomb paintings and Assyrian carvings, to Ancient Mayan art and Australian Aboriginal cave paintings. The animals have been connected with ceremonies and rituals, and in some places are considered to be divine. In Burma, tortoises were kept in the grounds of sacred pagodas and fed delicacies, while the second incarnation of the Hindu deity, Vishnu, is said to have been as a turtle. In many cultures it was believed that a turtle held the world on its back. In North America, the Mohawk tribe believed that earthquakes were caused by the turtle stretching. Some myths told that the world was held up by four elephants, and they, in turn, stood on the back of a turtle. The creator goddess, Nuwa, in Chinese folklore used the legs of a turtle to prop up the sky after the water god GongGong destroyed the mountain upon which it had been resting. In Greek mythology, Apollo turned into a turtle to woo Dryope, the daughter of Dryops, King of Eurytus, and Aphrodite was depicted with a turtle as a symbol of fertility. Turtles have been depicted on coinage and stamps. They have also been popular in heraldry. When you start looking, turtles are everywhere.

The confusion regarding turtles or tortoises lasts to this day, as in some countries – for example, the USA – all the species may be called turtles. In others, including the UK, ‘turtles’ refers to those that live mainly or partly in water, while tortoises are their land-based cousins. In this book, the UK version is used.

The title of the book could be regarded as a misnomer too, because tortoiseshell is not the shell of tortoises but comes from marine turtles. The use of the word tortoiseshell may have arisen because early English naturalists called turtles ‘sea tortoises’. It would, therefore, follow that their shells would be tortoise-shell.

Tortoiseshell has been used for a multitude of different things, and in many parts of the world. Mostly it has been used for adornment. The most common items made through the ages are combs, but boxes of some sort probably come a close second.

Today tortoiseshell is still part of our lives. Imitation tortoiseshell spectacle frames, combs and hair slides are everyday items. ‘Tortoiseshell’ is as popular as it has ever been. And turtles should be protected because it should not be forgotten that a turtle holds up the world.

Maggie Campbell Pedersen, April 2020

Acknowledgements

Only when putting pen to paper – or fingers to keyboard – do you realize just how little you know about a subject. So you start reading, and that results in a lot of questions. So you start asking, which also results in more questions, because every answer makes you more curious and wanting even more information.

As always, I have been amazed at how willing people have been to help and to share their knowledge. I have had meetings with museum conservators and curators, and I have contacted complete strangers by email. Never once was I turned away. I have also been met with immense patience; indeed, one or two people must, in the end, have logged on to their computers each day with fingers crossed that there wasn’t another email from me awaiting their attention.

The people to whom I owe thanks are too numerous to mention here. Some have helped with a single piece of information, some with an introduction to someone else, and some have given me many hours and a lot of advice. My gratitude is sincere to each and every one. I could not have written this without that help.

There are a few people who must be mentioned by name: Dr George Hughes of Cape Town, leading expert on marine turtles and their conservation, helped me to keep on track with information about turtles; Ulli Freyer, furniture restorer in Bern, Switzerland, spent a whole day talking with me about tortoiseshell; Stéphane Ciccione, Director at Kélonia Sea Turtle Observatory, Réunion, answered questions about farmed turtles; Dr Caroline Solazzo at the Smithsonian, Washington, introduced me to proteomics; and Prof. Julia Horrocks, University of the West Indies, Barbados, introduced me to hawksbill turtles at the Barbados Sea Turtle Project twenty years ago.

Thanks also go to Prof. Tom Higham, Oxford Radiocarbon Accelerator Unit; Ayako Naito, Chief Liaison Officer Gem-A, Japan; Michael Hügi, Director Swiss Gemmological Society; William Wold, Chairman Vereniging Gemma; Dr Tony Tucker, Dr Scott Whiting and Dr Bob Prince of the Marine Science Program, Department of Parks and Wildlife, Western Australia; Alexis Kugel, Galerie J. Kugel, Paris; Rui Galopim de Carvalho, Vice-President Sector A, CIBJO; Patrick Daly, Senior Gemmology Tutor at Gem-A; and my fellow gemmologists at Gem-A, the Gemmological Association of Great Britain.

At the museums, I am greatly indebted to the following: Iskander Breebart, conservator at the Rijksmuseum in Amsterdam, and Jan Dorscheild, also at the Rijksmuseum; Thijs Boers, curator at The Amsterdam Museum; Kolokesa Mahina-Tuai, Fuli Pereira and Sabine Weik at the Auckland War Memorial Museum; Rebecca Fisher and Yvonne Carrillo-Huffman at the Australian Museum in Sydney, and many people at The Victoria and Albert Museum in London, especially Joanna Whalley, Senior Metalwork Conservator.

There are always some mistakes in a book and I take this opportunity to apologize for them. They are entirely my fault.

Finally, I would like to thank my friends and my family for their patience with me while I have been engrossed in turtle and tortoiseshell research, especially my daughters Louise and Kathrine, who are not only patient but also never cease to be encouraging.

Maggie Campbell Pedersen, April 2020

Chapter 1

Turtle Species

Introduction

Marine turtles are reptiles. They belong to the order Testudines, which also includes tortoises and terrapins, though marine turtles are often referred to as chelonians, as they belong to the family Cheloniidae. Strictly speaking, turtles live almost entirely in the sea, terrapins live in fresh water, such as ponds or rivers, and often bask on land, and tortoises live entirely on land.

In some countries, all three types of reptile are called turtles, and in others, including England, ‘turtles’ refers to those that live mainly or partly in water, while tortoises are their land-based cousins.

Fig. 1.Paper-thin scutes from a tortoise.

Fig. 2.Sturdy scutes from a hawksbill turtle.

Turtles differ from tortoises in several ways, the most obvious being that they are not terrestrial. In order to move on land, tortoises have legs and feet, rather than flippers for swimming, and they have developed the ability to withdraw their extremities into their hard shells for protection. It is likely that attempts have been made to use the scutes from all the hard-shelled turtles and tortoises as tortoiseshell, but, with the possible exception of the radiated tortoise’s beautiful shell from Madagascar, there are no records of this being successful with anything other than some marine turtles. The keratinous covering on the shells of tortoises is generally very thin and would have little practical use to anything but the tortoise, where it acts as a protective layer (Figs. 1 and 2).

Fig. 3.Young green turtle (Chelonia mydas) near Barbados.

Marine turtles are found world-wide in tropical and sub-tropical waters. They live and forage in one area and migrate to another to mate and nest. After their nesting season, they return to their favourite foraging grounds. They repeat the migration throughout their lives, covering many thousands of kilometres in the process (Fig.3). Reptiles are often referred to as being cold-blooded animals, yet they have to maintain a certain temperature. Many animals, such as fish, marine mammals and marine turtles, are ectotherms. This means that they regulate their internal body temperature by responding to changes in the temperature around them. Turtles need the warmth of the water to function. If they get too cold, they slow down and eventually die, which is probably the reason why they can sometimes be seen basking in the sun. Research undertaken in the Persian Gulf has shown hawksbills that forage in the shallow waters there apparently get too hot in mid-summer when the surface temperature of the water can rise a few degrees, so they migrate to deeper water. After a month or two, when the temperatures drop again, they return to their favourite area in shallower waters. Only leatherback turtles are able to regulate their body temperatures to maintain a constant 30°C, so they can occasionally be seen foraging near ice floes.

Origin and Species

The origin of marine turtles is not totally clear. It is still being debated whether they are descended from the same animals as birds and crocodiles, or whether they descend from a form of lizard.

From fossil remains, it is reckoned that a proto turtle, which had a partial shell, existed about 250 million years ago. It is known that later turtles could grow to an immense size. The remains of one found in a coal mine in Colombia has been named Carbonemys cofrinii, meaning ‘coal turtle’. It was large enough to eat small crocodiles and had a shell that measured 172cm. Its estimated age is 60 million years. Older and bigger was Archelon ischyros, the largest marine turtle ever discovered. Found in South Dakota, USA, it was 4m long but is not thought to have had a shell and so resembled more today’s leatherback turtle.

Over millions of years, marine turtles have reduced in size but otherwise have not changed very much. The various families have split into different species but the majority are now extinct, so that today there are only seven extant species.

The leatherback turtle is the largest and is in a family of its own: Dermochelyidae, genus Dermochelys coriacea. It can grow to over 2m in length. Leatherbacks have no shell but a tough, leathery skin containing bony plaques.

The remaining six marine turtles all have hard shells and all belong to the family Cheloniidae. They are sometimes referred to as chelonians. Three of them have not been used for tortoiseshell: the little Kemps ridley turtle (Lepidochelys kempii); the olive ridley turtle (Lepidochelys olivacea), which is also small; and the flatback turtle (Natator depressus), which lives only around Australia.

Fig. 4.Loggerhead turtle (Caretta caretta). GEORGE HUGHES

The horny plates (called scutes) on the shells of the remaining three can be used as tortoiseshell. They are: first and foremost, the hawksbill turtle (Eretmochelys imbricata), which is famous for the quality of its tortoiseshell and has been the most used; the green turtle (Chelonia mydas), which has also been used for tortoiseshell but which is possibly more famous as a source of meat and the basis of turtle soup, and is called ‘green’ because it has a fat layer that is slightly green in colour; and the loggerhead turtle (Caretta caretta), the tortoiseshell from which was used only occasionally (Fig. 4).

Hawksbill Turtles (Eretmochelys imbricata)

Hawksbill turtles are found around the globe, though they stay almost exclusively in warm, tropical waters. They are the smallest and least abundant of the three species. Their size varies but, on average, they grow to about 90cm carapace length, weigh about 75kg and reach maturity at twenty-five to thirty years.

Fig. 5.Section of an unpolished hawksbill turtle scute, seen by transmitted light, causing the growth rings to show through.

Hawksbills have scutes that can grow to almost 1cm in thickness and have a random mottled pattern (Fig. 5).

The main breeding and nesting grounds for hawksbills are around the Caribbean and Costa Rica, the east coast of Africa, Madagascar, Saudi Arabia, the north-east coast of Australia around the Great Barrier Reef, and Indonesia, the Philippines and Papua New Guinea. They also nest in many other places, including the southernmost part of Japan.

As their favourite diet is sponges, they live and forage around coral reefs, where they keep the invasive species down, allowing the corals to flourish. The turtles can eat up to eight times their body weight in sponges per annum. Favourite foraging grounds are off the coasts of Panama, Nicaragua, the Bahamas, and the islands of Micronesia and Melanesia. Some turtles stay near their nesting grounds, but most migrate anything between 60 and 300km or more to their foraging areas.

Green Turtles (Chelonia mydas)

Greens are the largest of the three species and also the most numerous of all marine turtles. Again, their size varies but, on average, an adult reaches about 130cm and can weigh more than 210kg. It has been noted that captive-bred green turtles grow and mature much faster than those in the wild due to their artificial diet of specially prepared, nutrient-rich pellets, and can reach sexual maturity as early as five years old (Fig. 6).

Fig. 6.Young green turtle.

Green turtles are found in both tropical and sub-tropical waters. They nest in most of the same places as hawksbills, and in many more besides; for example, in Florida, Ascension Island, the Seychelles and the eastern end of the Mediterranean. There are very large nesting populations in Oman and the south-western Indian Ocean, especially on the scattered islands around Madagascar. There are also many in the Great Barrier Reef of Australia.

The mottled pattern of a green’s carapace is more defined than that of a hawksbill and often has a radiating pattern, but the scutes are thin.

The East Pacific green turtle is found along the coasts from Baja California to Chile. It has darker colouring on both its carapace and plastron, is slightly smaller and is sometimes called a ‘black turtle’.

There have been discussions about whether it should be classified as a different species or sub-species.

Greens are mostly herbivorous as adults, preferring to forage off-shore in shallower waters than hawksbills or loggerheads in order to find the sea grasses that comprise the bulk of their diet, though they also eat some algae and small animal prey, such as jellyfish. They tend to migrate between 200 and 800km to their feeding grounds, with a maximum distance recorded on a tagged turtle of 2,850km.

Loggerhead Turtles (Caretta caretta)

Loggerhead turtles can be almost as large as greens, with a maximum weight of about 200kg and a length of up to 110cm. Their average age at sexual maturity is reckoned to be about thirty-five years. Loggerhead nesting grounds are more widespread than those of hawksbills and greens. They nest in some of the same places as the other two species, but also further south on Africa’s east coast, on Australia’s west coast and as far north as Japan. They are the most prevalent marine turtle in the Mediterranean, but it is Florida that has the most nesting loggerheads. There is also a big nesting colony on Oman’s Masirah Island.

Loggerheads have thin scutes, like those of the greens, and have heavier pigmentation, giving a darker colouring with less distinct mottling on their carapaces.

Of the three species, loggerheads tend, on average, to migrate the furthest to their feeding grounds. Many choose the Atlantic Ocean from Brazil to Canada, concentrating on the area around the Bahamas and Mexico. They are also found in the seas around southern Africa and Madagascar, the Arabian Peninsula, and further to the Far East and Australia. Tagged turtles have been measured feeding 200–600km from their breeding areas, with a maximum distance measured of about 3,500km.

Hybrids

It is known that cross-breeding occurs between some turtles and that there are examples of hawksbill and loggerhead hybrids, especially around the coast of Brazil where their nesting activities overlap. Research is ongoing to learn more about them. Of the examples seen so far, they appear to pick up characteristics from both species; for example, the serrated edge of the carapace of the hawksbill and the larger head of the loggerhead. The quality and colour of their scutes has not yet been noted.

Turtle Anatomy and Life Cycle

Precisely how the turtle’s shell developed has puzzled scientists for centuries. It is an odd construction that, apparently, has not changed greatly for many millennia. The anatomy of the three turtles is very similar. They have a dorsal (back) shell called a carapace and a ventral (belly) shell called a plastron. Over the bony skeleton of both carapace and plastron is a layer of horny plates called scutes, beneath which is the dermis from which they grow. The horny material is keratin, which is an insoluble protein akin to nails, hair, beaks and claws (seeChapter 3