ANALYTICAL APPROACH
Mary Virginia Orna Department of Chemistry College of New Rochelle New Rochelle, N.Y. 10801
Thomas F. Mathews Institute of Fine Arts New York University New York, N.Y. 10021
For the art historian, chemical analysis of pigments serves two main purposes. It can confirm or deny the alleged attribution or dating of a painting based on comparison with the known painting practices of the artist or period. In addition, the analysis of pigments can have a broader, and perhaps a more profound, importance to the historian as a tool for understanding more about the artistic process itself. Although art historians are accustomed to relying primarily on formal analysis of style for describing the interrelationships of artists and schools, the task can also be approached from the point of view of the artists' materials. The continuity of workshop traditions can be tested in the artists' use of the same pigments over a period of time, whereas innovations in palette can be seen as a sign of a break with tradition. For example, it has been demonstrated that Tintoretto's reputation as an innovative colorist has a very real foundation in the way he employed his pigments (1). Not only did Tintoretto use the widest range of pigments available in Venice at t h a t time—four different blues, for example—he also used them in mixtures and layers quite unparalleled in the work of his contemporaries. Our project involved the study of medieval illuminated manuscripts through the application of small particle analysis techniques. The project started with Armenian manuscripts, which offered a special advantage in that most of them are dated and located by colophons or inscriptions, and has been expanded to include Byzantine and Islamic manuscripts. To date, the project has uncovered two forgeries (2, 3) by identifying pigments of modern manufacture in allegedly medieval manuscripts. In addition, more light has been shed on several art historical problems, including tracing lines of influence and interconnection between 0003-2700/88/0360-47A/$01.50/0 © 1987 American Chemical Society
Uncovering the Secrets of Medieval Artists
The Visitation of Mary to Elizabeth, p. 312 of the Glajor Gospel Book of UCLA, attributed to the fifth painter, T'oros Taronec'i. ANALYTICAL CHEMISTRY, VOL. 60, NO. 1, JANUARY 1, 1988 · 47 A
medieval centers of manuscript production and clarifying periods of known usage of several important artists' pigments. Several dozen manuscripts have been sampled and analyzed from museums and centers such as the Walters Art Gallery (Baltimore, Md.), the Freer Gallery of Art (Washington, D.C.), the Pierpont Morgan Library (New York, N.Y.), the New York Public Library, the special collections of the University of California at Los Angeles and the University of Chicago, the Armenian Patriarchiate of St. James in Jerusalem, and the Monastery of San Lazzaro, Venice. Some of the data and results have been published in representative journals (4-6). Rationale for the approach The analysis of pigments contained in illuminated manuscripts can be approached in a variety of ways. The final decision regarding approach must be made on the basis of availability of samples and equipment and the amount of information that can be gained. One creative approach to pigment analysis based on methods of physical examination is described by RoosenRunge and Werner (7,8), who analyzed the Lindisfarne Gospels. The heart of their method is a visual comparison of the various pigment surfaces contained in a manuscript with pigments manufactured according to the recipes of the major medieval painters' manuals. The prepared pigments were painted out on small pieces of parchment, and the microscopical structure of the pigments in the manuscripts was then compared with the known samples using polarized light supplemented by visual observation in ultraviolet light. Another approach was that of wholemanuscript neutron irradiation in a nuclear reactor followed by gamma ray analysis and autoradiography (9). The gamma ray analysis permits identification of the elements contained in the manuscript; the autoradiographical analysis provides the specific locations of these elements. A similar approach applied to objects of art historical interest is energy-dispersive X-ray fluorescence analysis, which permits nondestructive semiquantitative elemental analysis (10). All of these methods are nondestructive in that a manuscript remains intact after analysis, but some serious shortcomings accompany them. The method of Roosen-Runge and Werner involves making reasonably intelligent guesses based on several assumptions. The other methods involve removing the manuscript from its location and subjecting it to multiple handlings and neutron or another type of bombardment by high-energy radiation. But the
Figure 1. The Visitation of Mary to Elizabeth. The circles indicate locations from which samples were taken for analysis. B, Y, and G indicate the hues: blue, yellow, and green; 5 is the number of the painter; 312 is the number of the manuscript page. The other numbers are x-y coordinates in millimeters measured from the bottom left corner of the page.
most serious drawback of all is the fact that neutron activation analysis and Xray fluorescence only provide information regarding the elements contained in the pigments and none regarding their chemical formulas. Given the availability of samples from a manuscript, there is no substitute for the good old-fashioned methods of analysis of microscopic particles. Although the methods described above are nondestructive, taking pigment samples from a manuscript can be equally nondestructive. First, sampletaking does not require removal of the manuscript from its permanent location. Second, if the sampling is well planned, it is a one-time operation that need never be repeated. Third, sampletaking involves much less handling of the manuscript than do other methods.
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Fourth, only the samples, and not the entire manuscript, are subjected to high-energy irradiation. Fifth, the samples can be taken in such a way that the lacunae left by excision of the pigment particles are not discernible by the naked eye. However, the most compelling reason for taking samples is the wealth of information that can be obtained, including unambiguous chemical identification. Of course, it is also necessary to identify cooperative curators. Sampling procedure The manuscripts described in this work were sampled by the abstraction of pigment samples using a fine surgical scalpel and several sampling needles of varying fineness under a binocular microscope (magnification 40X). In
many instances, samples were taken from offsets—smudges of pigment that had transferred onto the opposite page—thus allowing for procurement of a relatively large amount of sample without disturbing the corresponding miniature. When samples were excised directly from the paintings, the lacunae were hardly discernible, even at 40 X magnification. Each sample was coded according to hue, folio number, and x-y coordinates in millimeters, taking the bottom outside corner of the manu script page as the origin. For example, a code of R.45v[35,65] identifies a red sample taken from folio 45 verso, 35 mm from the left edge and 65 mm from the bottom of the page. The loca tions of the samples were also marked on photographs made of each page in the manuscripts (Figure 1). The aver age size of the offset samples was 50— 100 μύα; the others ranged in size from 4 to 40 μπι. An attempt was made to sam ple the complete hue range in each manuscript. Hues were differentiated by both visual assessment and by com parison with color chips from The Munsell Book of Colors (11). Sample analysis
The samples were initially analyzed by polarized light microscopy and X-ray diffraction according to the methods outlined by McCrone and Delly (12, 13). The microscope was an Olympus POS-1 equipped for photomicrography in transmitted light. The opaque sam ples were photographed at 180X mag nification in reflected light on a Reichert Me F 2 metallograph. The X-ray diffraction patterns were obtained by mounting the sample particles on a
glass filament in a 114.59-mm diameter Debye-Scherrer powder camera and ir radiating with Cu-K a X-rays for 24 h at 30 kV and 15 mA. Samples found to be organic in na ture were subsequently analyzed by FT-IR (Analect Model AQS-20M) and were also subjected to the microchemical tests described by Hofenk-de Graaff (14). However, this method and its results will not be discussed in detail because its potential as applied to art historical problems has been previous ly reported (15). Results
As a result of the analysis discussed above, it has been possible to describe in some detail the history of pigment use in Armenia and to report initial results on the Byzantine manuscripts; the Islamic material is still being stud ied. Two very different palettes were observed in Armenia in the eleventh century: that of Greater Armenia and that of Lesser Armenia (east and west of the Euphrates). The palette of Greater Armenia was found to survive almost unchanged in the later Arme nian kingdom of Cilicia on the Medi terranean in the thirteenth and four teenth centuries. This "typical" Arme nian palette relied very heavily on mineral pigments (e.g., vermilion, orpi ment, and natural ultramarine); the typical Byzantine palette, on the other hand, was found to consist primarily of organic pigments. Several other obser vations were made: • Natural ultramarine as a blue pig ment and vermilion (natural mercury [II] sulfide) as a red pigment are com mon to all of the manuscripts, whether
Figure 2. Photomicrograph of the ultramarine used by the first painter (sample no. 1.B.17 [155,165] of the Glajor Gospel Book of UCLA). Magnification is 130X in transmitted light. This is a very high grade of ultramarine.
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Armenian or Byzantine. • Azurite (blue basic copper [II] carbonate) has been detected in several instances, but its use has been found to be limited only to fourteenth-century Armenian manuscripts, when it may have been imported from the West. • No true green pigment has been found in any of the manuscripts; the green hue was achieved by mixing blue and yellow pigments. • The purple hues were obtained by mixing varying amounts of vermilion with blue pigments. • Magenta, purple, and red hues, which were distinguishable both visu ally and through comparison by Mun sell chips, were chemically distinct. • Brown, flesh, orange, and olive tones were all achieved by skillful mix ing of more basic colors. For example, the flesh tones in several of the manu scripts were achieved by mixing vary ing amounts of vermilion, white lead (basic lead carbonate), organic yellow, and organic red. • The yellow pigment orpiment (ar senic [III] sulfide) was used extensively in manuscripts from Armenia but is ab sent from the vast majority of Byzan tine manuscripts. Discussion
The palette thus far established for Cilician Armenia shows a remarkable consistency from manuscript to manu script and within any given manu script. For example, several of the great Cilician gospel books are known to have been the products of collaborative work of several artists, but the range and quality of the pigments proved to be quite uniform. Analysis of a similar collaborative effort of five painters in a fourteenth-century manuscript from Greater Armenia (2), however, showed a widely differing palette and extremes of pigment quality from painter to painter. The ultramarine used by the first painter (Figure 2) is consistently of far better quality than the ultrama rine used by painters three, four, and five (Figure 3). The Cilician uniformity may indicate greater control in the manufacture of the pigments and the application of more rigid standards for the work of the individual artist. Unfortunately, until comparable data have been developed on contem poraneous manuscripts painted in Eu rope and the Islamic states, it will not be possible to situate exactly the pal ettes of Armenia and Byzantium with respect to other traditions. However, some interesting trends and contrasts can be observed. Although ultramarine is the standard blue in Armenia as well as in Byzantium, in Europe it seems to have been the exception. The pigment comes from mines located in presentday Afghanistan; therefore it was more readily available in the Near East than
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Figure 3. Photomicrograph of the ultramarine used by the fourth painter (sample no. 4.B.160 [120,65] of the Glajor Gospel Book of UCLA). Magnification is 130X in transmitted light. The grade of ultramarine in this sample is much poorer than that shown in Figure 2 and approximates the percentage of colorless matrix found in the poorest grade of ultramarine, known as ultramarine ash. PAT. PENDING
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in Europe, where it often cost more than gold and had to be contracted for separately in the commission of a painting (16, 17). At the same time, azurite seems to have been in short supply in Armenia. It is curious that the Near Eastern artists lacked a natu ral green and had to resort to mixtures, but in Europe the use of verdigris (a collective term for copper acetates of varying compositions and presumably imported from Greece—hence vert de grece!) can be dated to at least the thir teenth century. The use by the Chinese of malachite, Cu 2 C0 3 (OH)2, can be demonstrated as early as the ninth and tenth centuries. Having established the "typical" Ar menian palette, we can notice develop ment and innovation in its use. In the thirteenth-century Cilician kingdom, one begins to notice more extensive use of animal or vegetable pigments along with the traditional mineral pigments. More striking innovations appear in the work of a fifteenth-century artist whose palette we analyzed: one Khatchatur of Khizan, who expanded his palette to include realgar and smalt. Realgar, an orange pigment generally found in the same ore deposits as orpi ment, has the formula AS2S2. This pig ment is rare in Armenian manuscript illumination, because the traditional method of achieving orange hues con sisted of mixing vermilion with orpi ment (and organic yellow pigments) and shading the resultant hue with white lead until the desired tonality was obtained (3). Another rare pigment used by Khatchatur was smalt, a finely
52 A · ANALYTICAL CHEMISTRY, VOL. 60, NO. 1, JANUARY 1, 1988
ground cobalt-containing glass that produces a pale, transparent blue. Al though its discovery has been attribut ed to a Bohemian glassmaker of the mid-sixteenth century, a more recent review of the literature reveals that smalt may have been produced in the Near East several centuries before its alleged European discovery. The pres ence of smalt in Khatchatur's fif teenth-century manuscript seems to bear out this latter possibility. The scientific study of medieval painting is still in its infancy. Until we can define the range of materials and techniques used in the surrounding Is lamic principalities, the Crusader king doms, and the developing ateliers of Europe, the true measure of the inno vative techniques as well as the tradi tionalism of the Near Eastern painting schools thus far studied will remain an unanswered quantity. This work was supported in part by grants from the National Museums Act, the Faculty Fund of the College of New Rochelle, the New York Uni versity Research Challenge Fund, and the Hagop Kevorkian Foundation. References (1) Plesters, J. Presented at the Conserva tion of Paintings and the Graphics Arts, Lisbon Congress, London, England; 1972, pp. 153-60. (2) Orna, M. V.; Katon, J. Ε.; Lang, P.; Mathews, T. F.; Nelson, R. S., submitted for publication in Archaeol. Chem.—IV. (3) Schmitz, B.; Mathews, T. F., Institute of Fine Arts, New York University, 1985-87, unpublished results. (4) Orna, M. V.; Mathews, T. F. Stud. Conseru. 1981.26,57-72. Continued on p. 56
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(5) Cabelli, D. E.; Mathews, T. F.; The Journal of the Walters Art Gallery 1982, 40, 37-40, (6) Cabelli, D. E.; Orna, M. V.; Mathews, T. F. In Archaeol. Chem.—Ill; Lambert, J. B., Ed.; American Chemical Society: Washington, D.C., 1984; pp. 243-54. (7) Roosen-Runge, H.; Werner, A.E.A. In Evangeliorum Quattuor Codex Lindisfarnensis; Kendrick, T. D., Ed.; Urs Gras: Lausanne, Switzerland, 1960; Vol. 2, pp. 263-72. (8) Roosen-Runge, H. Farbgebung und Technik Fruhmittelalterlicher Buchmalerei; Deutscher Kunstverlag: Munich, F.R.G., 1967, Vol. 1, pp. 11-17. (9) Muether, H. R.; Balazs, N. L.; Cotter, M. J. Abstracts of Papers, 68th Annual Meeting of the College Art Association of America, New Orleans, La., 1980, p. 133. (10) Carriveau, G. In Archaeol. Chem.— ///; Lambert, J. B., Ed.; American Chemical Society: Washington, D.C., 1984, pp. 395-402. (11) The Munsell Book of Colors; Baltimore, Md., 1958. (12) McCrone, W. C; Delly, J. G. The Particle Atlas, 2nd éd.; Ann Arbor Science Publishers: Ann Arbor, Mich.; 1974, Vols. I-IV; 1978, Vols. V-VI. (13) McCrone, W. C. ; McCrone, L. B.; Delly, J. G. Polarized Light Microscopy; Ann Arbor Science Publishers: Ann Arbor, Mich., 1978. (14) Hofenk-de Graaff, J. H. Natural Dyestuffs for Textile Materials: Origin, Chemical Constitution, Identification; Central Research Laboratory for Objects of Art and Science: Amsterdam, The Netherlands, 1967, p. 13 ff. (15) Shearer, J. C; Peters, D. C; Hoepfner, G.; Newton, T. Anal. Chem. 1983, 55, 874 A-880 A. (16) Orna, M. V.; Low, M.J.D.; Baer, N. S. Stud. Conseru. 1980,25, 53-63. (17) Harley, R. D. Artists' Pigments; c. 1600-1835; Butterworths: London, England, 1970.
Developed from a symposium sponsored by the Divisions of Analytical Chemistry, Environmental Chemistry, and Nuclear Chemistry and Technology of the American Chemical Society ACS S y m p o s i u m S e r i e s N o . 3 6 1 338 pages (1988) Clothbound ISBN 0 - 8 4 1 2 - 1 4 4 S - X LC 8 7 - 3 0 7 3 5 US & Canada $ 6 4 . 9 5 E x p o r t $ 7 7 . 9 5 Order from: American Chemical Society Distribution Office Dept. 78 1155 Sixteenth St. N.W. Washington. DC 20036 or CALL TOLL FREE
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56 A
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ANALYTICAL
Evolution, Innovation, and Applications
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Thomas F. Mathews, a professor of art at the Institute of Fine Arts, previously taught at the Pontificio Istituto Orientale (Rome) and at the University of California, Los Angeles. His research interests include the history of Byzantine architecture, the iconography of medieval art, and the analysis of pigments in medieval manuscript painting.
CHEMISTRY, VOL. 60, NO.
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Mary Virginia Orna, a professor of chemistry at the College of New Rochelle, received her Ph.D. in analytical chemistry from Fordham University in 1962 and joined the New Rochelle faculty in 1966. She chaired the ACS Division of the History of Chemistry in 1983 and 1984 and received the 1984 CMA Catalyst Award.
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