R. Bellucci and C. Frosinini, “Cum suis debitis proportionibus”: Perspective and Geometry in...

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1. Appendix, docs. ix, xv.

“Cum suis debitis proportionibus”:Perspective and Geometry in Sassetta’s Borgo San Sepolcro Altarpiece

Roberto Bellucci and Cecilia Frosinini

Many art historians, though alert to questions of style and form, as well as to documentary and his-torical evidence, still have a difficult relationship with technique and the actual circumstances in which artworks were created. However, in the late Middle Ages and early Renaissance, technique and workshop traditions determined the choice of materials and methods, and thus also the final visual results, as much as or maybe even more than iconography, liturgy, or patronage. Sassetta’s Borgo San Sepolcro altarpiece may be considered an emblematic example of the union of tech-nique and style, of the inseparable relationship between the means and end, and of the necessities of workshop traditions and design.

Sassetta and his workshop had to face considerable challenges in taking on the commission of an altarpiece that not only had to incorporate a complicated iconographic program, but was also a physical structure of considerable complexity due to its large size and the fact that it was to be painted on both sides. The painting had to correspond to the dimensions of the high altar of the church of San Francesco in Borgo San Sepolcro, which was in an isolated position in front of the main chapel at such a distance from the walls that the altarpiece could not be anchored to them. Furthermore, the altarpiece was to be constructed and painted not in Borgo San Sepolcro but in Siena. Sassetta had to develop specific techniques to meet these strict requirements, techniques that in turn affected visual and stylistic choices. How and to what extent an artist achieved har-mony between technique and style is not always easy to determine, but such questions help to further understanding, not only of the attitude and methods of a single artist, but also of those of the period in which he lived.

In the case of the Borgo San Sepolcro altarpiece, the most difficult physical problem was the construction of a structure that was to be painted on both sides and that had to be made in parts for transportation and on-site assembly. Whereas cross-beams were usually applied to the back of one-sided polyptychs to hold the structure together, for double-sided altarpieces other systems of support had to be found. Moreover, since the Borgo San Sepolcro altarpiece could not be anchored to the walls, piers extending to the floor had to keep it upright. The construction of such a struc-ture, which had to correspond exactly to the dimensions of the area where the painting was to be installed, meant that the artist could rely on a solid base of technical skill and on the traditions of his craft. It also implied careful planning, and perhaps also while the wooden panels were being prepared, trips to the site.

In addition to the structural requirements, architectural considerations determined the con-struction. These last included the proportions of the picture fields and other elements such as moldings, colonnettes, socles, and carved decorations. Called fornimenti (furnishings) or finimenti (finishes) in the documents, these parts of the framing structure may seem ancillary, but they are paramount for the work’s overall visual impact, and were probably an aspect that Sassetta, the painter, as opposed to just the carpenter who constructed the complex, was closely involved in planning.

Sassetta declined to use a preexisting support that had been made for the friars of Borgo San Sepolcro in 1426 and which, indeed, was already prepared for painting, as it had a gesso prepa-ration.1 This decision may have been influenced by a variety of technical, formal, and economic

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Perspect ive and Geometr y in Sassetta’s B orgo San Sepolcro Altarpiece

2. Among the most famous documented cases of previously constructed wooden structures being employed for a polyptych are the altarpiece for the Pieve in Arezzo by Pietro Lorenzetti (Guerrini 1988), the polyptych by Piero della Francesca for the Augustinian church of Borgo San Sepolcro (Battisti [1992], vol. ii, pp. 611, 612, and for the hypothesis that the Franciscan structure rejected by Sassetta was reused by Piero for this altarpiece, Banker 2001), and the Pisa polyptych by Masaccio (Gardner von Teuffel 1977). Other authors who have clearly distinguished between the work of woodworkers and the painters are Gilbert 1977; Bomford et al. 1989, pp. 15, 16; Merzenich 1997; Frosinini 1999; and in all her studies, Gardner von Teuffel (assembled in 2005). There are other ex-plicitly documented cases of collaboration between painters and carpenters for the architectural structures of altarpieces. Neri di Bicci commissioned from Giuliano da Maiano an altarpiece (“1 tavola d’altare ... fatta e formata al’anticha ... chome apare per uno disegnio fatto al detto Giuliano di mia mano”; Neri di Bicci [1972], ricordanza 111, pp. 57, 58). In 1428, Ottaviano Nelli

provided Bartolomeo di Giovannino d’Angelo with the design for an altarpiece for the Confraternity of the Misericordia in Borgo San Sepolcro (Banker 1995, p. 28, doc. 2). In 1433, Antonio d’Anghiari provided Benedetto di Antonio Mattei with the design for an altarpiece for the church of San Giovanni Battista in Borgo San Sepolcro, which was later painted by Piero della Francesca and Matteo di Giovanni (Dabell 1984[a], pp. 86–88, doc. 9). De Marchi (2002, pp. 201, 202) also underscored the decisive role of the painter in collaboration with the carpenter. 3. If, in 1454–1470, Piero della Francesca reused the wooden structure made in 1426 for the Franciscans for his altarpiece for the Augustinians of Borgo San Sepolcro (Banker 2001, and see the chapter by Israëls [ii] in this book), Piero would cer-tainly have had to remove the preexisting ground and apply new gesso. An old preparation—in this case over thirty years old—would simply not have provided a good surface for gilding and paint. For the importance of a fresh gesso ground, see the chap-ter by Bellucci and Frosinini (ii) in this book. Further proof that Piero did not use the old ground is provided by the 1994

factors.2 The 1426 support, which was based on the polyptych by Niccolò di Segna in the local Camaldolese abbey, probably no longer satisfied either the artist or his patrons. The reasons for their dissatisfaction must have been of a visual or aesthetic nature that was important enough to cause them to reject the entire structure instead of simply making modifications to it. In addition, Sassetta may have made the decision not to use that altarpiece because he did not want to execute the painting in Borgo San Sepolcro. He had good reason to stay in Siena, where he had a workshop on which he could rely, as well as relationships with other craftsmen that he might need. And there he could also take on other commissions. There would have been numerous practical and economic disadvantages involved in moving the wooden structure to Siena, which would have meant taking it apart and reassembling it. Furthermore, the gesso ground was already several years old. Painting on a fresh preparation was undoubtedly preferable.3 By having the carpentry executed in Siena, Sassetta would have been able to supervise the division of the spaces for each

Fig. 304 X-radiographic detail of Sassetta’s Saint Francis in Glory (figs. 12.1, 12.5), with indications of the construc-tion of one of the arches of the pentafoil. The yellow arrows indicate the incised double line and the red arrow the hole left by the compass. (Drawing by Roberto Bellucci)

Fig. 303 (left) X-radiograph of Sassetta’s Saint Francis in Glory (figs. 12.1, 12.5), with indications of the incisions used to construct the pentafoil arch. (Drawing by Roberto Bellucci)

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examination of cross-sections from the panel of the Augustinian altarpiece that is in the Museo Poldi Pezzoli in Milan (Saint Nicola da Tolentino). There would have had to be a visible layer of soil deposited on the old ground and the layer that Piero first applied to the surface. However, such a layer of soil was not pres-ent in the cross-sections from the Augustinian altarpiece. In the 1440s, Piero had started to apply oil to his grounds, which can be clearly seen directly on top of the ground in the cross-sections illustrated by Di Lorenzo (1996[b], pp. 28–29). Those cross- sections are identical to those of other works by the artist pub-lished by Alexander and Gallone Galassi (1987), in which there is a layer of oil and no question of an old gesso ground having been used. The cross-sections and other unpublished

results of technical investigations of Piero’s Augustinian altar-piece are at the Opificio delle Pietre Dure, Florence (opd). See also Bellucci and Frosinini 1998, pp. 89–93. 4. Appendix, doc. xv. 5. It is not possible to correlate one or the other method to a specific function. In fact, the carpenter seems simply to have used whatever tool was on hand. Bellucci and Frosinini 2004[a], especially pp. 318, 319. 6. Bellucci, Frosinini, and Parri 2002, p. 194. 7. White 1973, pp. 356–358; Brink 1983; Castelli 1999, p. 61, and his chapter in this book; Merzenich 2001. 8. Bellucci, Frosinini, and Parri 2002, esp. p. 220. 9. Castelli, Parri, and Santacesaria 2006, p. 131.

section of the altarpiece, as well as the design of the frame, and this must have been an impor-tant factor in his decision to reject the old structure. Contractually, Sassetta was required to cover expenses relating to the installation of the altarpiece,4 and this may have triggered his refusal of the older structure, which he would have had to disassemble, transport to and from Siena, and then reassemble in Borgo San Sepolcro.

How the wooden supports of altarpieces were planned and executed within workshops has been extensively studied, and what has become particularly evident is that woodworkers and painters needed some competence in geometry, in certain cases almost to the level of that required of archi-tects, in order to design such structures. The general tendency to discredit artisanal work, which began in the sixteenth century, and the consequent separation in art history of the study of theory from that of technical skill, has undermined a proper understanding of the knowledge of geom-etry of medieval and Renaissance craftsmen; it was part of their overall cultural background. Art historians have sometimes used mathematical formulas to decipher measurements and spacing in order to reconstruct the overall geometric design of the carpentry of an altarpiece, but caution is needed in such undertakings, because during removal or disassembly of such works, panels may have been cropped, making it difficult to establish the original dimensions, and hence the original proportions, precisely. In the Borgo San Sepolcro altarpiece, an overall scheme is evident in how the picture fields relate to each other in the main tier: On both sides, the central panel is exactly twice as wide as the lateral panels, and on the back, the scenes from the legend of Saint Francis are half as high as the saints on the other side. However, indications of the precise planning that carpenters put into the production of altarpieces can be seen in the marks made with incisions5 or with charcoal and red sinoper (sinopia)6 that are often found on the areas of wooden panel sup-ports that are not covered by paint or gilding, as well as under the ground and paint.7 The most common markings are called chiamate and served to indicate where two adjacent sections of an altarpiece should be joined in assembly.8 But more design-based indications can be found in inci-sions that help establish the proportions of single panels, and also in the traces of compasses used to make the arched tops of the frames.9

X-radiography of the Borgo San Sepolcro altarpiece reveals traces of elaborate planning of the picture fields and frame on all the sections of the main tier, which to a large extent preserve the original framing elements; this corresponds to the above-mentioned methods of medieval carpen-ters. The woodworker made incisions with the aid of a compass (of which the central points are also visible) to compose the crowning pentafoil and trefoil arches of the panels (figs. 5 of Entries 7–20; figs. 303, 304). The design of these arches must have been studied beforehand to meet criteria of spatial proportions between the arches and the picture fields. Harmony in the crowning arches would balance the sometimes crowded pictorial compositions below, and would overcome the difference between the front face, consisting of depictions of individual saints, and the rear, with scenes of the Franciscan legend (plates i–vi). The proportions of the framing elements, which give a rhythmic delineation to the altarpiece’s various parts, serve to control the viewer’s perception of the entire complex. The careful planning of the polyptych resulted in a final impression of con-summate supervision and coherence. Thanks to the rare, relatively complete survival of so many fragments of so large a complex, it is possible to search for the common criterion that inspired its proportions.

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10. See the chapter by Bellucci and Frosinini (ii) in this book.

11. Horizontals passing through the intersections of the two sets of diagonals are visible in infrared reflectography (fig. 12.6).

The style of the main figures on the front side, which faced the lay congregation, is in a Sienese tradition that appreciated rich and ornate depictions, and which was certainly also well regarded in the cultured, although provincial, environment of Borgo San Sepolcro. For the large number of narrative scenes on the other side, however, Sassetta set about planning and executing his scenes in an almost obsessive manner. This is evident not only in the insistent use of perspec-tive in the Franciscan scenes (figs. 1 of Entries 13–20), but also in the geometric design of Saint Francis in Glory (fig. 12.1). Simple only in appearance, this last image came out of the observation that the panel and the area within it destined for the figure of the saint corresponded to two rect-angles, within the smaller of which the mandorla and the figure of the saint are perfectly inscribed (fig. 357).10 Using the diagonals of the two rectangles, the painter succeeded in establishing both a coherent spatial composition and a connection with the pentafoil at the top of the panel.11 Artistically speaking, this connection is completed by the foreshortening of the saint’s head and the slight convergence of focus of his upward-gazing eyes.

Through the use of focus of perspective, Sassetta obtained an emphatic spatial representation in the eight Franciscan scenes, in the predella with the legend of the Blessed Ranieri (figs. 1 of Entries 4–6), and to a lesser extent in the Passion predella (figs. 1 of Entries 1–3; see also plates i–vi). Had Sassetta’s goal been pictorial unity throughout the back side of the altarpiece, his per-spective would have to be considered only partially successful. The painter did not establish the

Fig. 305 Reconstructed perspectives of the scenes with the legend of Saint Francis and of the scenes with the legend of the Blessed Ranieri on the back of Sassetta’s Borgo San Sepolcro altarpiece. (Drawings by Roberto Bellucci)

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12. Saint Francis’s Vision (fig. 13.1) has two lateral vanishing points that each correspond to half of the scene. In Saint Francis Renounces His Earthly Father (fig. 14.1), the vanishing point is on the left, outside the picture plane, and coincides with the van-ishing point of the right half of Saint Francis’s Vision, originally to its left. The vanishing point in Saint Francis before the Pope (fig. 15.1) is on the left, outside the picture plane. The vanish-ing point in the Stigmatization (fig. 16.1) is on the right, outside the picture plane, and therefore, although the perspectives in the pair of scenes in the upper row, originally to the left of the Saint Francis in Glory, converge, in the pair of scenes in the row below, they diverge. The Wolf of Gubbio (fig. 17.1) has a vanishing point on the right, outside the picture plane. Saint Francis before the Sultan (fig. 18.1) has a central vanishing point. The Mystic Marriage (fig. 19.1) has an internal vanishing point, toward the left. The Funeral of Saint Francis (fig. 20.1) has a central vanish-ing point. See also figure 305 and plates ii, iv, vi. 13. The Miser of Citerna (fig. 4.1) has two vanishing points on

its central vertical axis. The Apparition to a Cardinal (fig. 5.1) has a lateral vanishing point coinciding with the left edge of the pic-torial surface, and the Liberation (fig. 6.1) has a vanishing point within the picture plane on the far right side. In the outdoor set-tings of the scenes of the Passion, only the Procession (fig. 3.1) has an architectural backdrop, which has an almost central van-ishing point. 14. “un modo che ella potesse venir giusta e perfetta, che fu il levarla con la pianta e proffilo e per via della intersegazione: cosa veramente ingegnosissima et utile all’arte del disegno”; Vasari 1550 and 1568 [Bettarini and Barocchi 1966–], vol. iii, p. 142. By the sixteenth century, perspective had become a mathematical and theoretical exercise rather than an aid to painting (as it had originally been conceived of by Brunelleschi, according to his biographer Antonio Manetti, and as suggested by his likely role as collaborator with Masaccio for the back-ground of the fresco of the Trinity in Santa Maria Novella in Florence. Vasari himself makes no mystery of his basic neglect

vanishing points of the single scenes in relation to each other, an approach that would have helped guide the viewer’s eye through the narrative sequence. Instead, the solutions that Sassetta adopted for the individual scenes are so different that it is obvious he was not interested in such overall unity (fig. 305).12 The same may be said of the predella scenes, which do not respect a consistent reading of perspective and do not have a shared vanishing point.13

Sassetta displayed an obsessiveness in laying out the compositions of each scene. He used numerous incisions, which unlike common workshop practice at the time, were not just for the architecture. Even on the relatively small pictorial surfaces, he devised the architecture and the setting with incisions that correspond to the composition as painted, but also with lines and arcs that only serve to construct the perspective. The artist incised the orthogonals on the gesso ground and marked every point of intersection, creating an extremely tight grid in which to place the major and minor elements of the composition. This type of perspective corresponds to what Vasari associated with Brunelleschi: “a way in which it [the perspective] could turn out right and perfect was to plan it out on the ground plan and profile and by means of intersecting lines. This was truly most clever and useful for the art of design.”14 It is also the method that Piero della Francesca described for drafting complex objects and architecture.15

Fig. 306 Line drawing of existing incisions in Sassetta’s Saint Francis’s Vision (fig. 13.1). (Drawing by Roberto Bellucci)

Fig. 307 Infrared detail of Sassetta’s Saint Francis’s Vision (figs. 13.1, 13.6), showing how the incisions are interrupted for the contour of the head of the poor knight.

Fig. 308 Line drawing of the reconstructed perspective and of the figures in Sassetta’s Saint Francis’s Vision (fig. 13.1). (Drawing by Roberto Bellucci)

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of the matter (“Ma del modo di tirarle [perspectival lines], poiché ella è cosa fastidiosa e difficile a darsi ad intendere, non voglio io parlare altrimenti. Basta che le prospettive son belle tanto quanto elle si mostran giuste alla loro veduta e sfuggendo si allontanano dall’occhio, e quando elle son composte con variato e bello ordine di casamenti”; Vasari 1550 and 1568 [Bettarini and Barocchi 1966–], vol. i, pp. 119, 120).

15. Piero della Francesca [1984], book i, chapter xii (“Da l’ochio dato nel termine posto il piano asignato degradare”), p. 75; Camerota 2001. 16. Bellucci and Frosinini 2005[b]. 17. See the respective chapters by Ravaud and Eveno, and by Bellucci and Frosinini (ii) in this book. 18. Israëls 1998, esp. pp. 442, 443, doc. 4.

In other early-fifteenth-century paintings, the detailed use of incisions for architectural structures shows that the perspective was first planned on paper, and then entirely reconfigured on the pre-pared panel, as opposed to transferred from the drawing.16 Sassetta instead carefully left in reserve the areas for the figures and worked his tight grid of incisions around them, a procedure that implies that the shape and position of the reserved areas had already been established before the perspec-tival lines were made in the gesso (figs. 306–308, 324a, 324b). With the help of patroni, or templates, Sassetta must already have outlined the figures on the gesso ground. This working sequence may be better understood by taking into account yet another unusual feature of the artist’s methods: The incised lines of the perspective were not done freehand but with a straightedge, even when the vanishing point where the lines converge is located outside the picture surface (figs. 309, 310). Such perspective could not be designed directly on the gesso ground, since vanishing lines converging outside the painted surface and laid in with a straightedge would inevitably have been obstructed by the applied molding (glued to the support during construction and gessoed with the rest). This observation and the fact that the figures were positioned first suggest the use of a transfer.

In infrared reflectography, traces left by the transfer of a spolvero, or pricked cartoon, are visible in almost all the scenes of the altarpiece (figs. 298, 313–318, 359, 360). Sassetta’s use of cartoons for whole compositions is unusual at this date, but is confirmed by the traces of pouncing in the large-scale saints of the Borgo San Sepolcro altarpiece. There the spolvero dots are close together, yet still farther apart than spolvero by other artists dating from the second half of the century.17 Also, a document exists indicating that he prepared a full-scale cartoon for the fresco of the Coronation of the Virgin at the Porta Romana in Siena. (For a detail of the fresco, see fig. 9.)18 The use of spolvero on panel had been preceded by that in fresco, in which it had served the design of decorative detail and of architecture. If Sassetta—versed in both fresco and panel painting—employed spolvero for the figures of his altarpiece, it is likely that he did so for the architecture, too.

Fig. 310 Digital infrared reflectogram of Sassetta’s Saint Francis’s Vision (figs. 13.1, 13.6), with indications of the reconstructed perspective and the figures. (Drawing by Roberto Bellucci)

Fig. 309 Line drawing with reconstruction of the vanishing points in Sassetta’s Saint Francis’s Vision (fig. 13.1). (Drawing by Roberto Bellucci)

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19. See the chapter by Billinge in this book, and see Entry 17, Changes in the Composition. 20. It should be born in mind that in the outdoor setting be-

hind Saint Francis’s father in Saint Francis Renounces His Earthly Father, the pavement is similar. 21. This confirms what is said by Carli 1957, p. 66.

Once Sassetta—who is also documented as a specialist in supplying drawings for sculpture, intarsia, and glass windows—had started to use spolvero for the figures of his compositions, he may then have explored the possibilities it offered for transferring perspectival designs. The method he employed for figures differed from that for perspective and architecture; for the latter, he seems to have selectively trans-ferred only the main points in his cartoons. Rachel Billinge observed that the dots that relate to the incisions and that are visible in the infrared reflectograms of the Franciscan scenes seem to be little holes full of dirt. Instead of proper spolvero, in these points the artist may have pricked the cartoon directly on the gesso ground. He then connected the dots on the ground by incisions made with a straightedge or a compass, or by drawing with a liquid medium (figs. 311, 312). Many of the dots served only for the perspective and not necessarily for the com-position as later painted; for example, in the choir stalls of the Miser of Citerna (figs. 318, 4.1). In the cross-vaults in the Funeral of Saint Francis (figs. 322, 20.1), the dots mark the intersections of the orthogonals and arcs incised for the complex perspective. These lines are often longer than the architectural elements, such as piers and ribs, the way they were later painted. Sassetta’s use of both templates and the more innovative pounced cartoons in the Borgo San Sepolcro altarpiece sheds new light on the history of technique and the passage from templates to cartoons in the fifteenth century.

Cartoons enabled Sassetta to construct the perspective of his scenes in a very careful way. This holds true not only for the feats of perspectival virtuosity displayed in his architectural structures (figs. 319–321), but also for the figures and objects that had to be placed within rationally depicted spaces. In one case, the perspective as planned was not used in the final composition. In the Wolf of Gubbio (figs. 17.1, 17.6), as visible in infrared reflectography, there originally was an elaborate grid in front of the city gate.19 This grid, possibly meant to be a pavement, has a perspective that is consistent with that of the painted figures and the city gate, demonstrating that Sassetta’s change of thought occurred in the final phase and probably not because he wanted to depict a different scene, but rather because he wanted to give this scene a different setting.20 Saint Francis Meets a Knight Poorer than Himself and Saint Francis’s Vision of the Founding of the Franciscan Order is a good example of Sassetta’s mastery of spatial representation (figs. 306, 308, 13.1). A complex network of incisions, visible in X-radiography and raking light, forms the loggia above the saint’s room and the castle with its flagpoles representing Saint Francis’s vision of the militant Church in the sky. This is one of two scenes in which Sassetta used two vanishing points on the same horizon, both of which are placed outside the picture plane. It is as if, by dividing the scene with its two subjects—the encounter with the poor knight on the left and the vision of the founding of the order on the right—vertically in two and by conceiving these two settings according to different ground plans, Sassetta has placed the viewer at the center and made it possible to look at each of the two scenes from a different viewpoint (fig. 308).21 Although its perspective is rather approximate, the Liberation of the Prisoners of Florence (fig. 6.1) also has two vanishing points that diverge.

Fig. 311 Infrared detail of Sassetta’s Saint Francis Renounces His Earthly Father (figs. 14.1, 14.6), showing the ocu-lus of the episcopal palace, constructed with the help of a cartoon transferred by spolvero or by pricking, which left three pounced dots or holes.

Fig. 312 Indications on the infrared reflectogram of fig. 311, showing the pounced or pricked and incised lines used to construct the oculus. (Drawing by Roberto Bellucci)

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Fig. 317 Infrared detail of Sassetta’s Miser of Citerna, showing pounced dots or pricked holes from the cartoon for the door of the church and entrance to the choir. (Drawing by Roberto Bellucci)

Fig. 313 Infrared detail of Sassetta’s Saint Francis Renounces His Earthly Father (figs. 14.1, 14.6), showing the base of one of the pilasters, with indications of the pounced dots or pricked holes from the cartoon used as a refer-ence point for tracing the incisions. (Drawing by Roberto Bellucci)

Fig. 316 Infrared detail of Sassetta’s Miser of Citerna, showing pounced dots or pricked holes from the cartoon for the arch of the transept.

Fig. 318 (right) Infrared detail of Sassetta’s Miser of Citerna, showing pounced dots or pricked holes from the cartoon used as reference points for constructing the per-spective of the choir stalls. (Drawing by Roberto Bellucci)

Fig. 315 Infrared detail of Sassetta’s Blessed Ranieri Shows the Friars the Miser of Citerna’s Soul Carried to Hell by Demons (figs. 4.1, 4.6), with indications of the pounced dots or pricked holes from the cartoon used as reference points for tracing the incisions of the architecture.

Fig. 314 Infrared detail of Sassetta’s Blessed Ranieri Shows the Friars the Miser of Citerna’s Soul Carried to Hell by Demons (figs. 4.1, 4.6), with indications of the pounced dots or pricked holes from the cartoon used as ref-erence points for the construction of the niche. (Drawing by Roberto Bellucci)

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22. Pope-Hennessy 1939, esp. pp. 25, 32–35, 58, 80, 110, 111; see also Longhi 1940, pp. 156, 168; Graziani (1948, p. 80) rec-ognizes the Madonna della Neve as Sassetta’s moment of most intense participation in “the great Florentine ideas about form and perspective,” and so does Carli (1957, p. 17), who further underscores the possible influence of Masolino and other “mi-nor masters,” such as the Master of 1419 (today identified as Battista di Biagio Sanguigni; Laurence Kanter, in Kanter and

Palladino 2005, pp. 227–230). 23. Israëls 2003[b], p. 126. 24. Ruda 1993, p. 23; Holmes 1999, pp. 14–15. 25. New documentation for Gentile da Fabriano in Siena will be presented by Gabriele Fattorini in a forthcoming publication; see also the chapter by Christiansen in this book. 26. Mancini 1882, pp. 287, 288.

In the Miser of Citerna (fig. 4.1), a special perspective serves to render the gable roof. Pictorial effect is achieved by using two vanishing points, one above the other on the vertical axis of the scene: one for the ties, or horizontal beams of the roof, and one for the braces, or diagonal beams. By assigning a lower vanishing point to the diagonal beams, a high viewpoint is suggested, which corresponds to the viewer’s place relative to the original low position of this predella panel within the altarpiece.

The Apparition of the Blessed Ranieri to a Cardinal (fig. 5.1) represents perhaps the most realistic setting in the polyptych. Although this scene is also divided into two narrative parts, Sassetta, aided by its horizontal format, succeeded in constructing the entire composition from a single lateral viewpoint and with a vanishing point within the picture plane on the far left side (fig. 323). The X-radiograph of the scene (fig. 5.5) documents the meticulous accuracy of Sassetta’s use of incisions that run all over the surface and are also there for the perspectival construction. It may be revealing of Sassetta’s mentality that, even though he prepared the composition on a paper cartoon, he repeated the perspectival construction with which he composed his scenes on the panel as well, as though he wanted to demonstrate the underlying concept behind the art of perspective.

Sassetta almost obsessively used a rational spatial plan for his compositions, which reveal his knowledge of Filippo Brunelleschi’s and Leon Battista Alberti’s applications of perspective. Ever since John Pope-Hennessy, art historians have posited a Florentine visit by Sassetta for his first large work, the altarpiece for the Sienese Wool Guild (1423–1425), for his Madonna della Neve (1430–1432),22 and finally, and to an even greater extent, Florentine influence for the Borgo San Sepolcro polyptych. On the other hand, Machtelt Israëls suggested that Sassetta and his contempo-raries could have been introduced to the rules of perspective during Brunelleschi’s visit to Siena in the late 1420s.23 It should also be noted that between 1428 and 1429, the Florentine painter Filippo Lippi served as subprior of the Carmelite convent of Siena.24 Sienese culture was well aware of contemporary Florentine artistic achievements; in 1401, two sculptors from Siena, Francesco da Valdambrino and Jacopo della Quercia, participated in the competition for the northern doors of the Baptistery of Florence, and in 1427, Donatello sent his bronze panel with the Feast of Herod for the Font of the Baptistery of Siena. Donatello’s work in particular was a demonstration of the latest innovations in spatial representation, with a composition based on Euclidian geometry. Already between 1423 and 1425, through Gentile da Fabriano, working in the city on his now-lost Madonna dei Notai, ideas about spatial rendering, even if less rational than those proposed by Brunelleschi, probably had reached Siena.25 Just as important may have been the Sienese visit of Alberti in the retinue of Pope Eugenius iv in 1443, following the conclusion of the Council of Florence.26

In Trecento Siena, artists like Ambrogio and Pietro Lorenzetti had attempted a pictorial depiction of rational space; Quattrocento artists such as Sassetta were very conscious of this earlier achieve-ment. Sassetta’s interest could therefore build not only on contemporary Florentine experiences, but also on local tradition. As attested by documentary sources, technicians with broad training played a key role in Siena’s urban development. In the thirteenth and fourteenth centuries, they designed Siena’s ingenious network of sewers and fountains to manage the hill town’s water. Other engineers were involved in metal casting (above all for cannons and bells, but also for sculpture, an activity closely linked to the rich mining in the area). A striking personality in the early fifteenth century is Mariano di Jacopo, called Taccola, who referred to himself as the “Sienese Archimedes,” and who wrote monumental technical works such as the De ingeneis (1433) and De machinis (1449). As a relative of the sculptor Jacopo della Quercia, he had ties with the humanist and artistic circles of Siena. To a certain extent, the affirmation seems valid that the drawings Taccola produced for his

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27. Galluzzi 1991.

treatises do not prove any affinity with the culture that distinguished Brunelleschi’s perspective, but instead testify to an encyclopedic medieval frame of mind.27 However, they do show interesting constructive concepts deriving from his activity as an engineer (according to the fifteenth-century definition of the term, a builder or an architect), which are the same used to design architectural structures in Renaissance paintings. Among these methods, measuring space by means of triangu-lation is particularly interesting. Triangulation is a geometric process of determining the location of a point by measuring angles to it from known points at either end of a fixed baseline. The dis-tance from the baseline can then be calculated as the perpendicular of a triangle with one known side (the baseline) and two known angles. This method was used for the measuring and rendering of buildings, and was elaborately described by Piero della Francesca in his late treatise on per-spective, De prospectiva pingendi, and its use in perspectival constructions in Piero’s painting has

Fig. 319 Line drawing of the reconstructed perspective and of the figures in Sassetta’s Saint Francis Renounces His Earthly Father, with a vanishing point on the left, outside the picture plane. (Drawing by Roberto Bellucci)

Fig. 320 Infrared detail of Sassetta’s Saint Francis’s Vision (figs. 13.1, 13.6), showing the construction of the loggia with the help of incisions and underdrawing.

Fig. 321 Infrared detail of Sassetta’s Saint Francis Renounces His Earthly Father (figs. 14.1, 14.6), showing the complex perspective of the architecture.

Fig. 322 Infrared detail of Sassetta’s Funeral of Saint Francis (figs. 20.1, 20.6), showing the perspectival construction of the vault.

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28. Bellucci 2000; Bellucci and Frosinini 2005[a]. 29. Longhi 1940, p. 178, and compare also 188, 189, notes 26 and 28. 30. Brandi 1949, p. 43; Israëls 2003[a]. 31. Longhi 1940, p. 178. 32. Conti and De Angelis 1976, pp. 98–101. 33. Christiansen 2005.

34. “il più singulare maestro di tempi suoi”; Baxandall 1972 [1988], pp. 26, 118–151. 35. “Fu Fra Philippo gratioso et ornato et artificioso sopra modo: valse molto nelle compositioni et varieta, nel colorire, nel rilievo, negli ornamenti d’ogni sorte, maxime o imitati dal vero o ficti”; Baxandall 1972 [1988], p. 118. See also Holmes 1999, p. 118; Christiansen 2005, pp. 50–55.

been revealed through infrared reflectography and X-radiography.28

The 1430s were a crucial time for painting in Siena, a period characterized by close attention to how Florentine artists were then investigating the issues of perspective and light. This inter-est is most pronounced in Sassetta, and also in another Sienese artist, Domenico di Bartolo. Both likely not only had contacts with Florence, but may also have had occasion from the 1420s onward to sojourn in that city.29 If Sassetta really was in Florence for a time—although there is no documentation for that—it would be interesting to discover in which workshop he might have been. Cesare Brandi and recently Machtelt Israëls have noted Sassetta’s affinity with Fra Angelico,30 and Roberto Longhi has noted correspondences with the work of Filippo Lippi, an artist whom Longhi described as bringing to fruition Masaccio’s legacy (“incari-cato dell’imbonitura”).31 Lippi is documented as being in Padua in 1434, but he had returned to Florence by at least 1437. Documents refer-ring to the execution between 1440 and 1447 of the Coronation of the Virgin for the high altar of Sant’Ambrogio (Galleria degli Uffizi, Florence)32 describe him as running a large workshop that also hosted non-Florentine craftsmen. These outsiders would have helped spread abroad the Florentine Renaissance manner,33 as attested by the praise accorded Lippi around 1490, long after his death in 1469, by the Florence-based agent of Gian Galeazzo Sforza, Duke of Milan, as

“the most singular master of his time.”34 Lippi’s style took into account Masaccio’s innovations and unadorned style, as well as Fra Angelico’s chromatism and Domenico Veneziano’s lumi-nosity. In 1481, twelve years after Lippi’s death, Cristoforo Landino wrote that “Fra Filippo was gracious and ornate and artful above all. His value lay in his compositions and variety, in his coloring, relief, and especially in ornamenta-tion of every sort, be it imitated or imaginary.” 35 Sassetta would have appreciated Lippi’s bal-ance between a novel use of space and late-gothic decorativeness. Whether Sassetta ever had a Florentine sojourn cannot now be answered, but the mere need for this hypothesis testifies to the artist’s mastery of rational spatial compositions that are almost Florentine, if it weren’t for his Sienese tendency toward the decorative.

Translated from the Italian by Diane Kunzelman

Fig. 323 Line drawing of the reconstructed perspective and of the figures in Sassetta’s Apparition of the Blessed Ranieri to a Cardinal (figs. 5.1, 5.5), with a vanishing point to the side of the composition. (Drawing by Roberto Bellucci)

Fig. 324a Detail of the servant at the door in Sassetta’s Apparition of the Blessed Ranieri to a Cardinal (fig. 5.1).

Fig. 324b X-radiographic detail of the servant at the door in Sassetta’s Apparition of the Blessed Ranieri to a Cardinal (fig. 5.5), showing how incisions are interrupted for the contour of the figure.

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