ABSTRACT—This article presents the results from a color infrared photographic study of the occurrence of ultramarine and azurite in a group of 13th- and 14th-century Sienese panel paintings. Color infrared film is a “false color film” that records the two visually similar blue pigments—ultramarine and azurite—as different, distinct, colors. This photographic technique was used to examine a number of early Sienese panels in European collections, including works by Guido da Siena, Duccio, Simone Martini, the Lorenzetti, and several later 14th-century masters.Two aspects of technique are explored in the article: the relative uses of ultramarine and azurite in three generations of early Sienese panel painters spanning the years ca. 1260–1345 and the creative use of the full range of grades of ultramarine by the later 14th-century masters. These findings are discussed in the context of the aesthetic and economic values placed on the two blue pigments during the late medieval and early Renaissance period. Ultramarine was more highly prized than azurite on account of its tonal richness, but it was also very expensive and, therefore, generally used more sparingly.

1 INTRODUCTION

WELL-PRESERVED or recently cleaned early Sienese paintings often stun modern viewers because of the brightness and variety of their color. It was the Sienese artist's aim to dazzle the beholder with the splendor of color just as with the shimmer of tooled gold surfaces. The most important of these colors, often reserved for the mantles of the Virgin and of Christ as Redeemer and Judge, were the blues.

Azurite and ultramarine were the two blues commonly used in early Sienese panel painting. Indigo, a very dark blue vegetable dye, although widely used in the 13th century, is generally found only in minor details of 14th-century paintings. In contrast, azurite—then commonly called azzuro d'Alemagna—was often used for draperies, particularly in works by Duccio and his circle. Azurite is a basic copper carbonate; the pigment is made by grinding and purifying samples of the naturally occurring mineral azurite (Gettens and FitzHugh 1966). To obtain an intensely colored pigment the particles must be left quite large; if they are ground too finely azurite looks gray.

As a blue, ultramarine was considered far superior to azurite. Because it was a tonally rich color, in contrast to the relatively flat and grainy azurite, ultramarine was usually preferred by panel painters. In addition, the hue of ultramarine—a slightly purplish-tinged blue—was held to be the ideal complement to vermilion and gold on panels. As Cennino Cennini's eulogy to ultramarine in his late 14th-century treatise on the arts reveals, a mystique surrounded this color:

Ultramarine is a color illustrious, beautiful, and most perfect, beyond all other colors; one could not say anything about it, or do anything with it, that its quality would not still surpass. … Let some of that color, combined with gold, which adorns all the works of our profession, whether on wall or on panel, shine forth in every object.

*(Cennini 1960, 36)

Aside from its tonally rich color, ultramarine was also considered an exotic, high-quality pigment because of its origins and price. Extracted from the semiprecious mineral lazurite (lapis lazuli), mined in the ancient quarries of Badakshan in an area now part of Afghanistan, it was imported from the Middle East via Venice (Plesters 1966). Furthermore, the process for making the pigment was laborious and time-consuming, and, as a result, the color was extremely expensive, sometimes even as costly as gold leaf. Originally the pigment was produced using a simple washing and grinding method that yielded a pale grayish-blue color. However, by about 1200, a new, more complex, but infinitely more effective method for extracting the blue color was developed. As Cennino Cennini explains, finely ground, high-quality lazurite is mixed with wax and resin to form a paste. Then this paste is immersed in a bowl filled with a weak lye solution (potassium carbonate) and poked with sticks to free particles of the blue mineral, which settle out. This process is carried out several times, releasing the most intense blue particles first and lower grades in subsequent extractions. The last extraction produces a gray pigment known as ultramarine ash. All grades were used (Cennini 1960, 36–39).

Although ultramarine was preferred for its coloristic qualities and associations, it was used much more sparingly than azurite in most early Italian workshops because of its great expense. In the mid-15th century in Florence, a period for which documentation exists, high-grade ultramarine cost 10 to 15 times as much as azurite and even low-grade ultramarine was about two-thirds the price of the finer quality pigment. These ratios are based on the prices paid by Filippo Lippi in the 1450s and by Neri di Bicci in the 1460s (Borsook 1975, 40–41; Bicci 1976, 270–71). It seems reasonable to assume that the price ratios in Siena in the late 13th and 14th centuries were not markedly different. Another indication of the exclusive nature of ultramarine is the fact that in early Renaissance painting contracts this pigment, like equally expensive gold leaf, was often specially supplied by the patron and considered as a separate payment. The amount of ultramarine used could determine, at least in part, the value and price of the painting (Merrifield 1849, 1:ccxi-ccxii; Lerner-Lehmkuhl 1936, 36).

The informative descriptions of painting projects in the work-diary of Neri di Bicci reveal how ultramarine was treasured and used in relation to azurite by this mid-15th-century but highly traditional Florentine artist. It is significant that Neri di Bicci describes not only where he put gold on his panels and what quality of gold he used, but often which blue pigment he used and where. Other colors are rarely mentioned and then only generally. For example, in the entry of July 5, 1466, devoted to the altarpiece of the Madonna and Child with Four Saints (to this day in San Michele, Arezzo) Neri says that he painted the mantle of the Virgin with ultramarine but used azurite for all the other blue areas (Bicci 1976, 273). Similarly, for the Trinity (San Niccol� Oltrarno, Florence, 1463) Neri used high-grade ultramarine of a value of 128 lire for the blue draperies but azurite for portions of the frame (Bicci 1976, 204). Apparently Neri saved ultramarine for the most important parts of his compositions, the blue draperies of the figures highest up on the religious hierarchy, usually the mantle of the Virgin.

2 IDENTIFICATION METHODS

THESE BLUES—ultramarine and azurite—so important to the medieval and Renaissance painter, often cannot be even tentatively differentiated by the naked eye when sampling and identification by microscopy are unavailable. Frequently they have been altered chromatically and even chemically by natural means or by human intervention. In many early Italian panels the Virgin's mantle has become very dark, almost black, and has a flat, opaque appearance. Any evidence of modeling is lost. For instance, the azurite mantle of the Virgin in Duccio's Rucellai Madonna (Uffizi, Florence, 1285) appeared dark with little trace of modeling, before the recent cleaning, as the Virgin's mantle in Simone Martini's 1333 Annunciation (Uffizi, Florence) does still. If azurite is present the blackening is usually the result of a darkened oil or resin varnish—a varnish which has darkened due to chemical processes occuring within the film—trapped between the large particles of the pigment. It is virtually impossible to leach out these varnishes, and attempts in the past using strong alkalis have only contributed to the darkening. On the other hand, old varnish films can give ultramarines a greenish quality. In other rare instances ultramarines look gray and grainy, perhaps due to the use, in past restorations, of acids, which decompose the pigment and result in color loss (Gettens and Stout 1966). One must be careful in distinguishing these ruined ultramarines from the deliberate use of the gray, low-grade form of the pigment, ultramarine ash. Chemical changes can also alter the color of blues. One change quite frequently found in the blue skies of medieval frescoes is the transformation of azurite into its green relative malachite, a change occasioned by the presence of water seeping through the walls and condensing on the wall surfaces (Mora et al., 1984, 66). Occasionally in mural decorations, the alteration of portions of azurite blue skies to the green basic copper chloride, paratacamite, in the presence of sodium chloride through contact with the chloride ion, has also been discovered (Gettens and Stout 1958).

Hence, it is often difficult to distinguish ultramarine and azurite with the naked eye based on a prior knowledge of how each color should look. And although the two pigments can be identified quite easily by chemical or microscopic means, this information is not always available from restoration or conservation laboratories in larger museums around the world, since many paintings have never been technically examined or sampled. Yet some photographic techniques are widely available, one of which has been in use since the early 1930s.

The first of these is the use of black-and-white infrared film, which can be obtained in formats of 35mm or 4 � 5 negative sizes from most photographic stores. Strong incandescent illumination or natural light emit sufficient quantities of infrared rays to irradiate pigments in a painting, and when combined with a yellow filter placed in front of the lens of the camera, the unequal infrared reflective properties of the various pigments are recorded. Marie Farnsworth in the 1930s was the first to experiment with the new film by recording the effects on known pigments. She found that azurite absorbed infrared light by appearing black on a positive print, whereas ultramarine blue reflected infrared rays and appeared light (Farnsworth 1938). This striking difference was immediately recognized by art conservators as a simple means of distinguishing the two pigments photographically, and soon thereafter experiments with the film made their way into the literature.

Then, in the early 1960s, color infrared film, which had been developed initially by the Eastman Kodak Company for the military to detect enemy camouflage, became commercially available. Whereas black-and-white infrared film has a slow emulsion speed and, therefore, requires strong auxiliary lighting, color infrared is much easier to work with. It can be used in daylight or with flash, making it possible to take this kind of photograph in many European galleries and churches. Like black-and-white infrared, color infrared film records the absorption or reflectance of infrared radiation characteristic of each pigment, but it does so in terms of color contrasts. Each pigment is recorded as a different and often distinct color, hence the characterization of this film as a “false color film.” Ultramarine blue appears cherry red, while azurite appears bluish. The reds are less easy to tell apart because vermilion is pale yellow and red lake is also yellow but a deeper shade (Olin and Carter 1970; Matteini et al., 1980; Matteini and Moles 1986, 189–93). For example, in a color infrared detail from Simone Martini's Orvieto Polyptych (Museo dell'Opera del Duomo, Orvieto, ca. 1320–23), the Virgin's ultramarine mantle shows up as red except for a small area of restoration that appears blue, indicating that the restorer used azurite. The red lake wrap of the Christ Child appears as yellow, and the Virgin's dress appears orange, suggesting that it consists of a mixture of red lake (yellow) and ultramarine (red) (figs. 1–3).

Fig. 1. Simone Martini, Orvieto Polyptych, Virgin and child, Italy, ca. 1320–23. Museo dell' Opera del Duomo, Orvieto. (Photo: Artini, Florence.)

Fig. 2. Simone Martini, Orvieto Polyptych, detail of Virgin and Child, Italy, ca. 1320–23. Museo dell' Opera del Duomo, Orvieto. (Color photo: author.)

Fig. 3. Simone Martini, Orvieto Polyptych, detail of Virgin and Child, Italy, ca. 1320–23. Museo dell' Opera del Duomo, Orvieto. (Color infrared photo: author.)

Color infrared film has important applications for the study of early Italian painting, as it enables the researcher to distinguish clearly when azurite or ultramarine were being used, an important distinction given the widely different values of the pigments on the contemporary market. For this study the photographic technique has been employed for the examination of a number of early Sienese panels in European collections. In the following discussion all determinations of blue pigments have been made, unless otherwise indicated, by the author using the technique of color infrared photography.

3 EXPERIMENTAL FINDINGS

IN THE mid-13th century, an extravagant use of ultramarine can be found in a number of large and seemingly prestigious commissions by Guido da Siena and his circle. Ultramarine blue is thickly applied for the mantle of the Virgin in the Madonna and Child Enthroned of 1262 by the San Bernardino Master (Torriti 1980, 23, color plate). This panel, now greatly cut down, must originally have been a huge, important work in the tradition of Coppo di Marcovaldo's Madonna del Bordone (Sta. Maria dei Servi, Siena) of 1261 and Guido da Siena's Palazzo Pubblico Maest� of ca. 1270 (Eglinski 1963, 205–12).

Extensive use of ultramarine is also found for draperies in two important dossals in the Siena Pinacoteca from the shop of Guido da Siena. In Dossal No. 7, attributed to Guido da Siena and datable ca. 1271–79, a thick coat of dark ultramarine was used for the mantle of the Virgin, and a lighter ultramarine, perhaps of a lower grade, was employed for the gown of St. John the Evangelist, the cloth sash of the Christ Child, and the inner portion of the Virgin's headdress (Torriti 1980, 26, color plate). The relative transparency of this lighter ultramarine in the painting and the weakness of its red translation in the color infrared photograph suggest that a lower grade ultramarine is present rather than a mixture of high-grade ultramarine and the opaque white lead pigment. For Dossal No. 6, ascribed to a close follower of Guido and dated ca. 1280, high-grade, dark ultramarine is again found for the Virgin's mantle, whereas a lighter ultramarine was employed for the gowns of St. Paul and St. John the Evangelist (Torriti 1980, 32, color plate). These dossals have both been cut down at either end; they each most likely had two extra figures of saints. In reconstructed form they would constitute the largest polyptychs to survive from the 13th century (Eglinski 1963, 125, 135–43). They represent two of the major commissions remaining from the period, and, as their materials indicate, they were very expensive to produce.

In contrast, the small Madonna and Child Enthroned (Pinacoteca, Siena), is a much more minor product from the workshop of Guido da Siena (Torriti 1980, 31, color plate). Predictably azurite was chosen for the Virgin's mantle. This miniature shop-replica of Guido's magnificent Palazzo Pubblico Maest� was clearly not a prestigious commission, as the small size, together with the inferior quality of workmanship and materials, suggests.

In general, a less extravagant use of ultramarine is found in paintings by Duccio and his workshop. Ultramarine is extensively used only in certain of the most important commissions, most notably Duccio's Maest� of 1308–11, which was adorned in the expensive fashion appropriate for the high altar of the Duomo in Siena. Ultramarine was identified in many locations on the Maest� when the work was examined and restored at the Istituto Centrale del Restauro in Rome, and no other blue pigments were found (Brandi 1959, 197). In addition, the predella panel of the Transfiguration from the Maest� was tested by scientists at the National Gallery in London, and Christ's robe was found to be ultramarine (Plesters 1966, 75). Ultramarine has also been identified in the mantle of the Virgin in Duccio's small, exquisite Triptych (National Gallery, London), indicating that some investment of materials was put into this high-quality work (Plesters 1966).

Nevertheless, for many of the altarpieces produced by Duccio and his workshop azurite was used, even for the Virgin's mantle. Beginning with an early work, the blue of the Virgin's mantle in the huge and magnificent Rucellai Madonna, commissioned for a chapel in the Florentine church of Sta. Maria Novella in 1285, has been identified during the recent cleaning as azurite (Del Serra 1990). The now-dark mantle of the Virgin in the Madonna and Child (Galleria Nazionale, Perugia)—formerly part of a polyptych most probably designed for the high altar of San Domenico in Perugia sometime after 1304 (Teuffel 1979)—is azurite, blackened by a layer of discolored varnish caught in the matrix of azurite particles. Given the importance of these two commissions the choice of azurite is quite surprising.

Similarly in Duccio's large Polyptych No. 47 of ca. 1311–18 (Pinacoteca, Siena), which came from the Ospedale di S. Maria della Scala, an important and prestigious Sienese institution, the darkened mantles of the Virgin and St. Agnes are azurite. The colors used in Polyptych No. 28 (Siena, Pinacoteca), which is usually dated just before the Maest� of 1308–11, are particularly difficult to interpret with the naked eye because of the distorting effects of a thick layer of yellow varnish (Torriti 1980, 51, color plate). However, color infrared photography reveals that the Virgin's mantle and the robe of St. Paul are azurite but that ultramarine has been used for the inner robe of St. Peter. The robe of the angel in the pinnacle above St. Peter is also ultramarine. Blue in combination with yellow is conventional for St. Peter; still, it is interesting to discover that in this altarpiece St. Peter is given preference over the Virgin through the selective application of ultramarine. Duccio may have had a reason for giving prominence and honor to St. Peter. Yet nothing is known for certain concerning the original location of this polyptych or its patronage. Stubblebine (1979, 1:65) tentatively associates the work with a polyptych that was on the high altar of the abbey church of San Donato in Siena, whereas White cautiously suggests a location in a Dominican institution because of the inclusion of Sts. Augustine and Dominic (White 1979, 63). Duccio's reasons for singling out St. Peter must, for the moment, remain a mystery.

Another interesting distribution of ultramarine and azurite occurs later in a work associated with the circle of Simone Martini, the Casciana Alta Altarpiece (San Niccol�, Casciana Alta, Pisa; on deposit in the Museo di San Matteo, Pisa) by an artist close to Lippo Memmi and datable to the early 1320s (Cannon 1982; Bagnoli et al., 1985). Although the mantle of the Virgin in this polyptych is azurite (with ultramarine added later for quite large areas of restoration), ultramarine is used for other draperies. The shadows of the Christ Child's creamy white tunic are ultramarine, and, as might be expected, the luxurious gown of the donor figure, lined with ermine, is ultramarine. On the other hand, the choice of ultramarine for the draperies of two of the pinnacle figures—the robe of St. Paul above St. Matthew and the mantle of Isaiah above St. John the Evangelist, both relatively unimportant parts of the composition—is more puzzling. Evidently ultramarine was not reserved for the mantle of the Virgin in every case. Other figures could be honored with a robe of ultramarine, or, occasionally, in an altarpiece of some value, ultramarine might be used somewhat haphazardly throughout the composition.

In the context of late 13th- and early 14th- century uses of blue pigments, the findings for works by Simone Martini and his shop that were investigated are the most illuminating. These works were the Pisa Polyptych of 1319 (Museo di San Matteo, Pisa), the Orvieto Polyptych(figs. 1–3) and the Madonna and Child with Redeemer and Angels from the early 1320s (Museo dell'Opera del Duomo, Orvieto), the Lamentation (Gem�ldegalerie, Berlin-Dahlem), which is one panel from the Orsini Passion Polyptych probably painted ca. 1334–37, and the Return of the Young Christ from the Temple dated 1342 (Walker Art Gallery, Liverpool) (Contini and Gozzoli 1970, color plates). Ultramarine was used almost exclusively for the blue draperies in these works. Even the blue or partially blue draperies of the small figures along the predella of the Pisa Polyptych are ultramarine. The only exception is the robe of St. Paul in the Orvieto Polyptych, painted with azurite. Furthermore, the ultramarine used in these paintings seems to be consistently of a high grade. Lighter blues, because of their opacity and the pure light blue rather than gray quality of their appearance, seem to have been produced by the addition of lead white to high-grade ultramarine rather than by using ultramarines of lower quality.

Such extensive use of superior quality ultramarine is not totally unusual among Simone's predecessors in Siena. We did discover a heavy use of ultramarine in important commissions produced by the workshop of Guido da Siena and his circle in the period ca. 1260–80. Nevertheless, in the products of artists from the generation directly preceding Simone—paintings from the workshop of Duccio—ultramarine was used more sparingly, reserved for the most expensive projects.

Significantly, the lavish use of ultramarine found in Simone Martini's paintings also stands apart in relation to the use of blues by his contemporaries in Siena, the Lorenzetti and their circle. Color infrared photography indicates that Pietro Lorenzetti used high-quality ultramarine for the Virgin's mantle in the large and elaborate Carmine Altarpiece of 1329 (Pinacoteca, Siena) (Torriti 1980, 97, color plate). But in the somewhat later and more ordinary Polyptych of San Giusto (Pinacoteca, Siena), probably by a close follower of Pietro, the Virgin's mantle and the light blue robes of Sts. Peter and Paul are predominantly azurite (Torriti 1980, 105, color plate). In this case, the slightly purplish appearance of the robes of Sts. Peter and Paul on the color infrared photographs suggests that a small amount of ultramarine blue may have been layered over the azurite. This technique may represent an economy measure: the thickness and intensity of the blue was ensured with less expenditure of ultramarine. The technique has been identified by Plesters in a number of later Venetian Renaissance paintings and according to van Os is “a common technique in early Flemish painting” (Plesters 1966, 64; Os et al., 1978, 16).

It is perhaps surprising to discover that the mantle of the Virgin in Ambrogio Lorenzetti's Annunciation of 1344 (Pinacoteca, Siena) is an intense, high-grade ultramarine, as this panel seems to have been commissioned for the Office of the Biccherna in Siena, a relatively unprestigious location (Torriti 1980, 125, color plate). Other findings for works from the shop of Ambrogio Lorenzetti are less puzzling. Azurite was chosen for the Virgin's mantle in two medium-sized and moderate commissions, the Sta. Petronilla Altarpiece datable ca. 1340 (Pinacoteca, Siena) and the Serre di Rapolano Madonna and Child also of ca. 1340 (Pinacoteca, Siena) (Torriti 1980, 110, 120, color plates).

As regards the later 14th-century Sienese painters, the most interesting feature discovered is their creative use of the full range of grades of ultramarine. In Bartolomeo Bulgarini's St. Peter Enthroned with Sts. Paul and John the Evangelist of ca. 1340 (Pinacoteca, Siena), where a substantial amount of fine-quality ultramarine is used for the blue and purple robes of St. Paul and the blue lining of St. Peter's mantle, low-grade ultramarine ash appears for the grayish lining of St. John the Evangelist's mantle (Torriti 1980, 134, color plate). Similarly, in Luca di Tomm�'s St. Anne Altarpiece, dated 1367 (Pinacoteca, Siena), a dark, high-grade ultramarine is employed for the mantle of the Virgin, and a lighter, medium-grade is found for the robe of St. Agnes. A third color variation is produced by using gray ultramarine ash with the addition of a small amount of red lake for the mantle of St. Anne in the altarpiece (Torriti 1980, 157, color plate). A technical quotation provides another interesting example: Pietro Lorenzetti's use of ultramarine ash for two figures in his Birth of the Virgin of 1342 (Museo dell'Opera del Duomo, Siena) painted for the major altar dedicated to St. Savinus in the Siena Cathedral, was imitated by Paolo di Giovanni Fei in his later painting of the same subject (Pinacoteca, Siena) datable ca. 1380–90 (Torriti 1980, 180, color plate). In addition, several other instances of the use of a variety of grades of ultramarine have been detected, most notably in the Polyptych No. 51 (Pinacoteca, Siena), a joint work by Niccol� di Ser Sozzo Tegliaci and Luca di Tomm�, where high-grade ultramarine is found for the Virgin's mantle and lower-grade for the mantle of St. Thomas, and in Jacopo di Mino Pellicciaio's Polyptych no. 58 (Siena, Pinacoteca), where dark, fine-quality ultramarine is used for the mantle of the Virgin and a poorer quality, lighter variety for the mantle of St. John the Baptist and the inner robe of St. Augustine (Torriti 1980, 151, 145, color plates).

4 CONCLUSIONS

FROM THE findings of this study we can begin to trace patterns of the occurrence of ultramarine and azurite in early Sienese panel paintings. As the data collected indicate, the more costly blue pigment, ultramarine, was generally found in most abundance on the large, prestigious altarpieces of the period. However, the choice of ultramarine rather than azurite varied, sometimes considerably, from artist to artist and period to period. During the earliest decades under scrutiny, ca. 1260–80, ultramarine was used quite extravagantly in a number of large commissions from the shop and circle of Guido da Siena, but by the next generation, ca. 1285–1315, we see a considerable drop in use. Ultramarine is included only in the most e1ite paintings produced by Duccio's shop, and in four large and relatively important altarpieces azurite was the primary blue, chosen even for the Virgin's mantle. One possible explanation, which requires further investigation, is that the discovered drop in the use of ultramarine resulted from a rise in price due to a decline in availability of the imported pigment.

For the third generation of Sienese painting the interpretation of the evidence is more straightforward. Simone Martini stands apart from his contemporaries in his heavy and almost exclusive use of high-grade ultramarine. The high quality of his materials cannot help but reflect his success as an artist and the consequent prestige of his commissions. Simone clearly took pride in using the best that was available and was fortunate enough to be able to afford to do so.

This study has also drawn attention to the creative ways in which Sienese artists, particularly those of the generations following the Black Death, exploited the coloristic potential of the variety of grades of ultramarine blue. Artists such as Luca di Tomm� in his St. Anne Altarpiece took pleasure in the decorative display of the different tones of the precious pigment across the surface of their panels.

Finally, and perhaps of most general value and interest, there is our heightened awareness of the symbolic way in which ultramarine could be employed in early Sienese images. As Michael Baxandall has pointed out in relation to 15th-century paintings, “the exotic … character of ultramarine was a means of accent that we, for whom dark blue is probably no more striking than scarlet or vermilion, are liable to miss” (Baxandall 1988, 11). Baxandall draws our attention to one particularly instructive example: in Sassetta's St. Francis Renouncing His Heritage (National Gallery, London), one panel from the Sansepolcro Altarpiece of ca. 1442, the gown that St. Francis takes off and leaves behind is a luxurious robe painted in ultramarine, and thus the gesture of discarding it is symbolic of Francis's entire renunciation of worldly goods for a spiritual life of poverty. We could add to this a similar example from another panel in this altarpiece: in The Whim of the Young St. Francis to Become a Soldier (National Gallery, London) the outer robe that Francis generously gives to a poor man is painted with ultramarine blue and glazed red lake shadow tones in order to simulate a lavish, and extremely valuable, velvet (Wyld and Plesters 1977).

In the Sienese 13th- and 14th-century altarpieces investigated in this study the expensive pigment, ultramarine, was usually reserved for the mantle of the Virgin, a traditional gesture of honor on the patron's and painter's part. And yet, as we have discovered, this was not always the case. Ultramarine might also be used to single out another significant protagonist in the composition. The figure of St. Peter in Duccio's Polytych No. 28 was accented in this way, as was the male donor in the Casciana Alta Altarpiece. Through the use of ultramarine the painters of these altarpieces, presumably on instruction from the commissioners, highlighted and drew attention to a favored saint and a donor-patron. It was a purely artistic means of paying respect.

ACKNOWLEDGEMENTS

THE AUTHOR would like to acknowledge the very generous assistance of Norman Muller, Hayden Maginnis, and Megan Holmes in the preparation of this manuscript. Furthermore, without the cooperation of the staff of several European art galleries the photographic research for this study would not have been possible. I would like to thank, in particular, the curatorial and support staff of the Pinacoteca in Siena; Monsignor Rosatelli of the Museo dell'Opera del Duomo in Orvieto; Erich Schleier and Claudia Laurenze of the Gem�ldegalerie in Berlin-Dahlem, and Julian Treuherz and Xanthe Brooke of the Walker Art Gallery in Liverpool.

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AUTHOR INFORMATION

CATHLEEN HOENIGER is assistant professor of art history at Queen's University in Kingston, Ontario, where she teaches the history and techniques of Italian Renaissance art. She received an M.A. in the history of science from the University of Toronto in 1983 and an M.F.A. (1986) and Ph.D. (1989) in art and archaeology from Princeton University; she wrote her Ph.D. dissertation on the painting technique of Simone Martini. Her current research areas include the technique and aesthetic of Sienese Gothic painting and the history and theory of restoration. Address: Queen's University, Department of Art, Kingston, Ontario, Canada, K7L 3N6.

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