Butterworths Series in Conservation and Museology Series Editors : Arts and A rchaeology Stephen G Rees- Jones Courtauld Institute of Art, University of London Architecture Derek Linstrum Institute of Advanced Architectural Studies, University of York US Executive Editor: Norbert S Baer, New York University, Conservation Center of the Institute of Fine Arts Consultants: Sir Bernard Feilden David Bomford National Gallery, London C V Horie Manchester Museum, University of Manchester Published titles: Artists' Pigments c. 1600-1835, 2nd Edition (Harley) Conservation and Exhibitions (Stolow) Conservation and Restoration of Works of Art and Antiquities (Kühn) Conservation of Building and Decorative Stone (Ashurst, Dimes) Conservation of Glass (Newton, Davison) Conservation of Historic Buildings (Feilden) Conservation of Library and Archive Materials and the Graphic Arts (Petherbridge) Conservation of Manuscripts and Paintings of South-East Asia (Agrawal) Conservation of Marine Archaeological Objects (Pearson) Conservation of Wall Paintings (Mora, Mora, Philippot) The Museum Environment, 2nd Edition (Thomson) The Organic Chemistry of Museum Objects (Mills, White) The Textile Conservator's Manual (Landi) Related titles: Manual of Curatorship Materials for Conservation Museum Documentation Systems Materials for Conservation Organic consolidants, adhesives and coatings C.V. Horie Keeper of Conservation The Manchester Museum Butterworths London Boston Singapore Sydney Toronto Wellington (g PART OF REED INTERNATIONAL P.L.C. All rights reserved. No part of this publication may be reproduced in any material form (including photocopying or storing it in any medium by electronic means and whether or not transiently or incidentally to some other use of this publication) without the written permission of the copyright owner except in accordance with the provisions of the Copyright, Designs and Patents Act 1988 or under the terms of a licence issued by the Copyright Licensing Agency Ltd, 33-34 Alfred Place, London, England WC1E 7DP. Applications for the copyright owner's written permission to reproduce any part of this publication should be addressed to the Publishers. Warning: The doing of an unauthorised act in relation to a copyright work may result in both a civil claim for damages and criminal prosecution. This book is sold subject to the Standard Conditions of Sale of Net Books and may not be re-sold in the UK below the net price given by the Publishers in their current price list. First published 1987 Reprinted 1990 (with corrections) © Butterworth & Co (Publishers) Ltd, 1987 British Library Cataloguing in Publication Data Horie, C. V. Materials for conservation: organic consolidants, adhesives and coatings. — (Butterworths series in conservation and museology). 1. Art objects — Conservation and restoration 2. Museum conservation methods I. Title 069.5'3 N8560 ISBN 0-408-01531-4 Library of Congress Cataloging inP ublication Data Horie, C. V. (Charles Velson) Materials for conservation. (Butterworths series in conservation and museology) Bibliography: p. Includes index. 1. Coatings. 2. Adhesives. 3. Art—Conservation 1 and restoration. I. Title II. Series. TP156.C57H67 1987 667'.9 87-13830 ISBN 0-408-01531-4 Composition by Genesis Typesetting, Laser Quay, Rochester, Kent Printed and bound by Hartnolls Ltd, Bodmin, Cornwall Preface The conservation of historic materials requires the application of a wide range of knowledge and skills. The aim of this book is to provide background information on one aspect of conservation treatments: the properties of organic consolidants, adhesives and coatings as they affect the treatment of objects. The variety of film-forming and binding materials, together with associated materials such as oils, is not covered by a single descriptive term. The inadequate word 'polymer' or 'resin' will often be used to encompass these materials. The vast number of commercial polymers and formulations creates considerable scope for harmful as well as beneficial changes in the practice and philosophy of conservation. Polymer science has increased our insight into polymer properties, offering the potential for valuable improve- ments in treatments and the materials used. It is my hope that the reader will assess the use of both new and old materials on objects more rigorously. This review comes at the end of an era in conservation practice. In the past, materials were applied in a traditional manner, frequently with no evaluation of the merits or consequences of the addition. When new, synthetic materials were introduced com- mercially, these were used in the same role, often without much evaluation because they appeared to be better. Testing of the industrial products was later carried out, sometimes thoroughly, in order to rank them in suitability for particular roles. This is the phase of development which I hope is passing. In its place, treatments are being developed, incorporating materials with appropriately specified properties, designed to fulfil a defined conservation need. Conservators must know about the added material and its effects on objects before making a decision on whether, and how best, to incorporate a material into a treatment for the object. Part I outlines the properties of polymers that are important in the interaction of polymers with objects. Chapters 1 and 5 provide a qualitative introduction and summary of the scientific basis for V vi Preface defining and assessing those properties which are covered in the intervening chapters. Part II provides a detailed consideration of individual polymers, their properties and uses in conservation. Most polymer types that have been used in the conservation of objects are included. At the end of the book are appendices which summarize data referred to in the text. There are various introductory texts in this field for conservators (Crafts Council, 1983; Feller et ai, 1971; Anon, 1968). Many books are available for schools and the general public which outline the concepts and properties of polymers. More detailed reference books which assume some knowledge of chemistry include Brydson (1982), Roff and Scott (1971) and Mark et al (1964ff). The reader is assumed to have access to publications of the International Institute for Conservation. Polymers that have been adequately described in those publications have been given a slighter treatment here to avoid duplication. Conclusions 1. The interactions between objects and polymers, etc. are ill-understood. Assuming that the object is the primary concern of the conservator, consolidants, adhesives and coatings should be applied only when necessary to the survival of the object. They should not be used as an alternative to proper packaging, environmental control, etc. Given the difficulties of removing polymers, they should be applied sparingly. 2. One of the most difficult tasks of a conservator is reversing the conservation treatment of an object before starting new stabilization treatments, etc. Publication of past treatments, assessments of their effects and reversal methods is rare but most welcome to the conservator who must treat objects with comparable problems. Conservation is dependent on the material history that survives. The history of conservation, which is rarely written, is an integral part of conservation studies. 3. Most commercial polymers are produced for industrial applications that are ephemeral by conservation standards. Conservators both past and present have used products whose suitability is untested. A few new products specified and tested for conservation are coming on to the market, but their composition remains proprietary. These must be viewed with the suspicion held for any commercial material. There is Preface vii sufficient information available to enable formulations to be developed to conservation standards and revealed in the public domain. These recipes would reduce the need for commercial products of unknown composition and variability. Acknowledgements The impetus for the writing of this book was given to me by Professor R. G. Newton and I wish to thank him and Mrs J. Newton for their support in the early stages of its formation. The need for a conservation text on polymers, etc. has been made clear to me by students of conservation at various institutions who, by their interest and questions during lecture courses, have prompted me to look more closely at the problems of objects and the treatment of them. Miss L. Bacon, Professor S. Rees-Joncs, my wife (Dr D. Kenyon) and Professor W. J. Feast have kindly read through portions of the text and suggested valuable improvements both in style and content. The data on individual products has been collated from information supplied by their manufacturers. The ready supply of data sheets and samples of the products from all the manufacturers listed in Appendix 5 enabled the compilation of the tables and, in some cases, the evaluation of properties important for conserva- tion. I was pleasantly surprised by how many manufacturers provided advice and unpublished data on their products, so increasing insight into their application for conservation. I wish to thank the following for advice and data which helped to clarify specific points or wider issues: Dr R. L. Feller, Dr S. G. Croll, Mr G. Berger, Dr E. P. Mel'nikova, Professor Dr K. Ueberreiter, Dr J. Winter, Professor W. C. Wake, Professor J. D. Ferry and Dr N. Tennent. Preface vii sufficient information available to enable formulations to be developed to conservation standards and revealed in the public domain. These recipes would reduce the need for commercial products of unknown composition and variability. Acknowledgements The impetus for the writing of this book was given to me by Professor R. G. Newton and I wish to thank him and Mrs J. Newton for their support in the early stages of its formation. The need for a conservation text on polymers, etc. has been made clear to me by students of conservation at various institutions who, by their interest and questions during lecture courses, have prompted me to look more closely at the problems of objects and the treatment of them. Miss L. Bacon, Professor S. Rees-Joncs, my wife (Dr D. Kenyon) and Professor W. J. Feast have kindly read through portions of the text and suggested valuable improvements both in style and content. The data on individual products has been collated from information supplied by their manufacturers. The ready supply of data sheets and samples of the products from all the manufacturers listed in Appendix 5 enabled the compilation of the tables and, in some cases, the evaluation of properties important for conserva- tion. I was pleasantly surprised by how many manufacturers provided advice and unpublished data on their products, so increasing insight into their application for conservation. I wish to thank the following for advice and data which helped to clarify specific points or wider issues: Dr R. L. Feller, Dr S. G. Croll, Mr G. Berger, Dr E. P. Mel'nikova, Professor Dr K. Ueberreiter, Dr J. Winter, Professor W. C. Wake, Professor J. D. Ferry and Dr N. Tennent. To my father Many of the materials mentioned in this book are hazardous to the operator or other people and property. Although some hazard information has been provided, the responsibility for ensuring the completeness or accuracy of the appropriate hazard information is the responsibility of the person undertaking the process. The mention of a material or process does not constitute a recommendation for its use on objects - usually the reverse. The author and publisher accept no responsibility for the consequences of the application of information or opinion expressed in this book. 1 Introduction 1.1 Use of resins in conservation Resins are used for many purposes in the conservation of objects: Consolidants Adhesives Coatings Moulding Casting Support stands Display and storage materials. This list is ranked according to the intimacy of contact with the object. The closer the contact, the more likely the object is to be affected by the polymer properties. In the first four categories the resin is applied to the object rather than the other way around. These are therefore of greater concern. In conservation it is an important discipline to study an object before one works on it. One should: (a) Find out what is wrong with the object. (b) Discover the cause of the defect. (c) Decide on the type of action. (d) Choose the appropriate method and materials. Neither (a) nor (b) are discussed in this work, but both (c) and (d) are determined by the potential and limitations of the available materials. The possible roles that the resin will play in the conserved object must be examined closely. Resins frequently serve two purposes at once. When sticking friable pottery, the adhesive may also consolidate and strengthen the edges. When coating loose paint, the varnish will both cover the paint flakes and stick them to the substrate. These dual roles may be of great importance when the time comes to reverse the treatment. Now the role(s) of the material have been stated, the required properties may be specified. In the real world one can never satisfy 3