Conservation Research 1996/1997 STUDIES IN THE HISTORY OF ART • 57 • Monograph Series II Conservation Research 1996/1997 National Gallery of Art, Washington Distributed by the University Press of New England Hanover and London Editorial Board Distributed by the University Press of ROSS M. MERRILL, Chairman New England, 23 South Main Street, SHELLEY STURMAN Hanover, New Hampshire 03755 E. RENÉ DE LA RIE SHELLEY FLETCHER Abstracted and indexed in BHA (Bibliography of the History of Art) Managing Editor and Art Index CAROL LEHMAN ERON Conservation Research is a periodic Manuscript Editor publication of the National Gallery of Art, ANN HOFSTRA GROGG Washington. The primary objective of Conservation Research is to report regularly Editorial Coordinator on the research and technical studies pursued JANICE GRUVER by the conservation division of the National Gallery of Art Production Editor ULRIKE MILLS ISSN 0091-7338 ISBN 089468-264-4 Designer CAROL BEEHLER Cover: Kazimir Malevich, Vanity Case, detail, 1913, oil on wood. State Tretiakov Gallery, Copyright © 1997 Trustees of the National Moscow Gallery of Art, Washington All rights reserved. No part of this book may be reproduced without the written permission of the National Gallery of Art, Washington, D.C. 20565 This publication was produced by the Editors Office, National Gallery of Art, Washington Editor-in-Chief, Frances P. Smyth The type is Trump Medieval, set by Artech Graphics II, Inc., Baltimore, Maryland The text paper is 128 gsm Japanese matt Printed in China Contents 7 Preface ROSS M. MERRILL 9 Azo Pigments: Their History, Synthesis, Properties, and Use in Artists' Materials BARBARA H. BERRIE and SUZANNE QUILLEN LOMAX 35 Recalling the Past: Evidence for the Original Construction of Madonna Enthroned with Saints and Angels by Agnolo Gaddi MARY BUSTIN 67 A Technical Examination, Investigation, and Treatment of a Fifteenth-Century Sienese Polychrome Terra-Cotta Relief PENELOPE EDMONDS 93 Renaissance Portrait Medals by Matteo de' Fasti: A Study of Their Casting Materials LISHA DEMING GLINSMAN 109 Kazimir Malevich's Paintings: Surface and Intended Appearance ANN HOENIGSWALD 127 Jan Steen's Painting Practice: The Dancing Couple in the Context of the Artist's Career MICHAEL PALMER and E. MELANIE GIFFORD 157 Contributors Preface uring the course of development of the con- well as Penelope Edmonds' discussion of the servation division of the National Gallery of conservation of a Renaissance polychrome DArt, scientific research has gained an impor- and gilt terra-cotta relief. Lisha Deming tant role. The scientific research department Glinsman's report on the results of x-ray flu- was established with the initial goal of assist- orescence analysis highlights a unique pat- ing conservators with analytical support. As tern in Matteo de7 Fasti's casting materials of analytical services to conservation treatment portrait medals. The painterly techniques of became routine, conservation scientists ex- Kazimir Malevich are discussed by Ann panded their activities to study the materials Hoenigswald, and those of Jan Steen are pre- and construction of works of art, producing sented by Michael Palmer and E. Melanie technical and scientific studies about the Gifford. Gallery's collections or works on loan. Although the publication of research re- For the conservators and other staff mem- sults may be routine in many other fields, bers motivated to learn more about the ob- the role of author is relatively new to many jects they work with, their research, in some conservators. As the part played by conserva- cases, has been conducted as an extension of tion in the museum environment grows and their regular responsibilities. Additionally, matures, conservators and conservation sci- both conservation scientists and conservators entists increasingly will make their research are increasingly incorporating their knowl- available to a wider audience through publi- edge of art history into the methodology of cations such as this. their investigations. The essays in this volume address a range of subjects that have been under recent study by the conservation division. Barbara H. Berrie and Suzanne Quillen Lomax collabo- rated to apprise conservators of the properties of azo pigments, which are widely used in artists' materials and commercial applica- tions. Of interest to both specialists and the museum visitor is Mary Bustin's investiga- tion of the frame elements and construction ROSS M. MERRILL of a trecento altarpiece by Agnolo Gaddi, as Chief of Conservation, National Gallery of Art 7 Arylide (Hansa) Yellow, PYi Toluidine Red, PR3 Diarylide Yellow, PYi4 Naphthol Red, PR22 Diarylide Yellow, PYi4 LitholRed, PR49:1 Diarylide Yellow, PYi2 Red Lake C, PR53:1 Diarylide Yellow, PY83 Lithol Rubine, PR5y:pr57:1i Diarylide Orange, POi3 Red2B, PR48:i BONRedC, PR52:i BARBARA H. BERRIE and SUZANNE QUILLEN LOMAX Azo Pigments: Their History, Synthesis, Properties, and Use in Artists' Materials n this century synthetic organic pigments materials, general information on azo pig- have dominated the colorant market. Thou- ments and dyes is included; however, our sands of such pigments have been prepared, focus is primarily on the azo pigments that some designed for specific applications, and are more widely used and are employed in i ' it has been estimated that by 1971 synthetic manufacturing artists materials. organic pigments occupied a 49 percent mar- Azo pigments containing one —N=N— ket share of artists' pigments.1 About 80 per- group are called monoazo pigments, while cent of the manufactured pigments are azos,2 those with two azo linkages are called disazo those that contain the azo linkage (—N=N—). pigments. Pigments with three azos are Representatives of azo dyes and pigments properly called trisazo, and those with four appear throughout the color spectrum, al- are tetraazo compounds, although some- though most are red, orange, or yellow (fig. i). times both are called disazos. Structural They are used as pigments in printing inks studies have shown that some solid state azo (both flexographic and gravure), paints (archi- pigments exist exclusively in a ketohydra- tectural, automotive, general industrial, and zone form;4 however, they are convention- artists7), plastics, rubber, textiles, crayons,3 ally represented by the azo form. and colored chalks. The classical azo pigments, which have Understanding the properties of these col- provided bright colors at low cost, are charac- orants is important in choosing the most terized by relatively poor lightfastness or sta- appropriate techniques for conservation, exhi- bility to heat and solvents. High-performance bition, and preservation of works of art, since azo pigments have been introduced since the stability and light sensitivity of these 1960 to meet the demands of more stringent materials must be considered. applications. However, the possible presence A great deal of information concerning of classical azo pigments, many of which are azo pigments exists in the chemical and used today, on numerous works of art should industrial literature, but it is not readily be taken into account when considering available to conservators. The aim of this their conservation and exhibition. A descrip- essay is to present a summary of this infor- tion and discussion of the general synthesis mation, with an emphasis on pigments used of the azo pigments and their properties with in artists' materials. (See appendix i for a respect to their structural similarities and i. Selected masstone glossary of terms.) Since contemporary artists differences follow. In addition, a brief history azo pigment color chips use a wide range of products not limited to of the subclasses of azos and notes on their Dominion Colour, Inc., 7 Atlanta, Georgia traditional or even nontraditional artists uses and permanence are given. 9 Terminology and Nomenclature 2. Silk swatches, five of which are colored with azo Azo colors were first developed for dyeing dyes: (fig. 2). They were sometimes called ice col- no. 7, bright crimson, with Violamine A 2 R (Meister, ors because ice was used during their synthe- Lucius, and Bruning) sis to keep the reaction mixture cold. Azo no. 10, crimson, with Azo- dyes, which are prepared from primary aro- Rubine S (Actien. Anilin. matic amines such as aniline, were also Fabrik. Berlin) known as aniline colors. Compounds from no. 13, dark crimson, with Bordeaux S. (Actien. Anilin. coal tar were used in the manufacture of Fabrik. Berlin) azos, so they were sometimes called coal-tar no. 14, rose scarlet, with colors. Investigation of the chemical struc- Brilliant Croceine MOO tures of these materials has led to the gen- (L. Cassella and Co.) eral term "azo" pigments, now in use. no. 15, scarlet, with Crystal Scarlet 6R (L. Cassella As pigments are introduced to commerce, and Co.) 5 they are assigned a Colour Index generic no. 16, scarlet, is dyed with name and number as well as a five-digit the nonazo dye, Ponceau 4RB (Actien. Anilin. Fabrik. Colour Index number. The Colour Index Berlin) generic name relates to the application of From George H. Hurst, Silk Dyeing, Printing, and Finishing (London, the colorant; for example, P stands for pig- 1892), pi. 2 ment, along with a description of the hue, such as Y for yellow or R for red.6 A sequen- tial number, referred to as the generic num- ber in the Colour Index, is also assigned to each colorant. For example, Hansa Yellow G is can be found in the Colour Index.& 3. Sample tube of assigned the generic name and number PYi, Commercial products, including artists' Grumbacher Red. The azo while Orthonitroaniline Orange is assigned pigment in the oil paint is materials, are often described by vague Naphthol AS-D (PRi 12) and the name and number POi. terms, such as "azo yellow" or "gamboge is labeled to indicate that The Colour Index number indicates the the paint conforms to ASTM hue." It is usually possible to discover the standards for quality and chemical classification of the pigment or precise identity of the colorants from the lightfastness dye, as series of numbers have been assigned to particular colorants that are chemically related.