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Workshop Practice Revealed by Two Architectural Reliefs by Andrea Della Robbia

2019; University of Chicago Press; Volume: 54; Linguagem: Inglês

10.1086/707572

2169-3072

Wendy Walker, Carolyn Riccardelli,

Building materials and conservation

Previous articleNext article FreeWorkshop Practice Revealed by Two Architectural Reliefs by Andrea Della RobbiaWendy Walker and Carolyn RiccardelliWendy WalkerConservators, Department of Objects Conservation, The Metropolitan Museum of Art Search for more articles by this author and Carolyn RiccardelliConservators, Department of Objects Conservation, The Metropolitan Museum of Art Search for more articles by this author PDFPDF PLUSFull Text Add to favoritesDownload CitationTrack CitationsPermissionsReprints Share onFacebookTwitterLinked InRedditEmailQR Code SectionsMoreRecent conservation treatment of two Della Robbia architectural reliefs in The Metropolitan Museum of Art revealed fingerprints, tool marks, coded numbering systems, and an apparent nonchalance with handling clay that provided fresh insight into the dynamic human engagement and mastery of the material that is characteristic of the Della Robbia workshop. The backs and sides of reliefs that are often hidden from the viewer—because they are framed, situated in niches, or mortared into a wall or ceiling—contain information that can lead to a deeper understanding of the creative process, perhaps more directly than any other source. During the critical early stages of conservation treatment, which are predominantly activities of observation and examination, conservators may rely on microchemical tests or high-tech imaging techniques to aid the eye. They also depend on their apprehensive knowledge to assess an object. By feeling the weight, the texture, the relative temperature of a surface, or the sound an object makes when tapped, they gain insights into how things are made and have been treated over time.As the observations in the following sections will show, this concept of combining technical and hands-on knowledge relates not only to the work of the conservator, but also to the workshop practice of Della Robbia. While their artisanal tradition had some technological basis, it was heavily rooted in practical knowledge, an understanding of materials based on vast experience that was passed down from master to apprentice, perhaps with the most closely guarded secrets expressed orally.During the Renaissance, clay used for sculptures did not originate from standardized combinations of raw materials as it does today; it was excavated from the earth and processed manually before using. The famous Della Robbia blue glaze, a technological wonder at the time, can vary significantly in hue even within the same object, indicating that mixing the glaze, perhaps one of the most technical aspects of ceramics, was based more on experience than precise formulas. Firing the kiln was done completely by eye, and depended on the skill of the kiln master who could judge the firing temperature by the color of the kiln’s interior. Technical innovations were sprung from artisanal traditions and a reliance on craft—not on science in the modern sense of the word. Successful completion of each step in the ceramic process was required before moving on to the next.Andrea Della Robbia At The Metropolitan MuseumThe Metropolitan Museum began acquiring Della Robbia glazed terracotta sculptures in the early twentieth century. Among the many magnificent pieces at the Museum, Saint Michael the Archangel (fig. 1) and Prudence (fig. 2), both created by Andrea della Robbia about 1475, are two of his most exceptional works. The present article describes discoveries made during the conservation treatment of these two sculptural reliefs, which arose for very different reasons: one following an accident, and the other on the occasion of an exhibition focused on Della Robbia sculpture. Before coming to the conservators in the Department of Objects Conservation, the Saint Michael lunette was installed above a doorway in a gallery of fifteenth-century sculpture and decorative arts. Prudence was in storage and had not been exhibited in more than twenty-five years. Through the circumstances of their treatments, these two works have rightly regained their position as some of the finest expressions of Renaissance sculpture at the Museum.fig. 1. Saint Michael the Archangel after treatment, and before mounting. Andrea della Robbia (Italian, 1435–1525). Saint Michael the Archangel, ca. 1475. Glazed terracotta, 31⅛ × 61⅞ in. (79.1 × 157.2 cm). The Metropolitan Museum of Art, Harris Brisbane Dick Fund, 1960 (60.127.2)fig. 2. Prudence after treatment, secured on new mounting system. Andrea della Robbia. Prudence, ca. 1475. Glazed terracotta, Diam. 64¾ in. (164.5 cm). The Metropolitan Museum of Art, Purchase, Joseph Pulitzer Bequest, 1921 (21.116)Overview of Della Robbia Workshop and PracticeAndrea della Robbia (1435–1525), the second in the long line of the distinguished Florentine family, was trained by his uncle Luca and furthered the development of their increasingly famous glazed terracotta sculpture. While Luca della Robbia (1399/1400–1482) invented the technique, giving rise to an entirely new and widely valued art form, Andrea expanded their production to include works for architectural use on a grand scale. In time, the workshop was passed to Andrea’s sons, of whom Giovanni and Girolamo were most notably active. The family business continued successfully until these descendants passed away, Giovanni in 1530 and Girolamo in 1566. Within a relatively short time thereafter, the Della Robbias’ carefully guarded technological secrets were lost.Luca was a leading Florentine sculptor initially trained and celebrated for his work in stone and bronze. Sometime in the 1440s he began to experiment in clay and became famous for his novel use of glazes to decorate terracotta sculpture.1 His first important commission was The Resurrection (1442–45), followed by The Ascension (1446–51), each located above the northern and southern sacristy doors in the Cathedral of Santa Maria del Fiore, more commonly known as the Duomo, in Florence.When Saint Michael the Archangel and Prudence were produced, Andrea was about forty years old and had been working alongside his uncle Luca for more than twenty years. The workshop, which was also the Della Robbia residence, was located on Via Guelfa in Florence, about a ten-minute walk from the Duomo. By then Luca had stopped working due to ill health, and when he died in 1482, Andrea inherited half the house and the business, eventually becoming sole owner. Even before Luca’s death, Andrea took the operation to the next level, increasing the fame and productivity of the workshop and passing the knowledge to his own children.2About 1475, Andrea and his workshop were in the midst of several major commissions, two of which were the Museum’s Saint Michael the Archangel and Prudence, the latter of which was likely part of a larger decorative scheme including the other cardinal virtues, Justice, Temperance, and Fortitude.3 The lunette and tondo are large, both about 5 feet (155 cm) in diameter and weighing 220 and 775 pounds (100 and 350 kg), respectively. They were created as architectural elements to be installed above doors or mortared into walls, for example. One of the most extraordinary features of Della Robbia’s glazed terracotta is its durability, even in outdoor environments. Many of the Della Robbia works found on facades throughout Florence have been in place for more than five hundred years, such as those of the Ospedale degli Innocenti and Orsanmichele. In fact, the glazed surface of the Saint Michael lunette is in remarkable condition despite having been installed on the exterior of a church and exposed to the elements for more than three hundred years.In order to produce large glazed sculptures such as these, many steps are required to transform raw clay into a strong ceramic body covered in fields of shiny, colored glazes so characteristic of the Della Robbia workshop. The Della Robbia clay was mined from a secret location along the banks of the Arno River and carefully processed. Larger works were initially modeled in one piece, in a simplified form suitable for mold making, importantly, without undercuts. The work was then strategically cut into pieces. For example, the Saint Michael lunette was cut into twelve sections in such a way that the divisions run inconspicuously along drapery folds or at elevation changes within the relief ’s composition.Next, a plaster mold was made from each clay section. Once the plaster hardened, the clay model was removed from the mold, a process that destroyed the original work. Then, an even layer of fresh, soft clay was pressed into the molds, and over the course of several hours water from the clay was absorbed by the porous plaster, causing the clay to shrink slightly and separate from the mold. The newly molded sections were extracted from the plaster and the surface was smoothed, adding clay where needed to build out relief not provided by the mold forms, then worked with tools to bring expression to the composition.The still-soft sides were paddled inward to create V-shaped voids between sections. The sections were then dried slowly to lessen the risk of warpage, and once bone-dry, they went into a kiln and were fired to approximately 1,832°F (1,000°C). The sections emerged from the bisque firing as baked clay at this stage; raw glaze slurries could be applied by brush in separate fields of blue and white. Finally, the prepared sections were fired again, to a slightly lower temperature this time, as was necessary for glazed terracotta. The work emerged with a blue and white glaze, dimpled and satiny with a slightly uneven gloss.4Regarding Saint Michael the Archangel and Prudence, it is likely that Andrea conceived, sculpted, and divided the original sculptures, then added finishing touches to complete the masterworks. His workmen fulfilled the tasks of making the plaster molds, filling, and removing the clay when set, perhaps even glazing and firing. When this entire process was first accomplished in the fifteenth century, the brilliant blue-and-white glazed terracotta made the Della Robbia workshop famous, establishing a family practice that would be active for more than one hundred years.Saint Michael the ArchangelSaint Michael is presented with wings outstretched, wearing the armor of God, a mighty sword in one hand and in the other, a scale weighing the virtue of souls. He gazes off to the left with a serene yet sorrowful expression. Modeled in high relief, Saint Michael’s graceful stance, his wings, the dramatic lion’s head on the pauldron, the winged head embellishing the cuirass, and the naturalistic folds of his garment convey a sense of physical presence and spiritual power. The simple yet dazzling palette of blue and white further accentuates the exquisite rendering of the work.Saint Michael the Archangel is the leader of all angels and of God’s army against evil; his qualities are courage, strength, and mercy (for those who deserve it). He is regarded and prayed to as a protector against evil as well as a healer of the sick. Depictions of Saint Michael have evolved through the ages. Often presented in full armor valiantly battling and defeating the dragon as described in the Book of Revelation (12:7–8), he was also known as the angel who would weigh the souls of the dead for their ultimate judgment and verdict. Here, Saint Michael is depicted simply with his sword and scales. Andrea chose to represent him this way, no longer as the angel at war against Satan, but rather the angel of divine justice and compassion.5The Saint Michael lunette was made about 1475 to be installed over the main entrance on the exterior of the church of San Michele Arcangelo in Faenza, Italy.6 Set over a doorway through which the faithful would pass, the figure’s serene expression could be interpreted in two ways: the repentant may be comforted, but a sinner might feel his dispassion and potential judgment.When acquired by the Museum in 1960, the lunette’s twelve interlocking sections were mounted on a heavy plywood panel with a gilded frame (fig. 3). It was displayed in various galleries, until its most recent setting above a doorway in Gallery 500, also known as the Quattrocento Gallery, where it stayed for twelve years. In the early hours of July 1, 2008, it fell to the floor and landed on its back, still contained within the wooden mount. The lunette’s sections were secured by T-shaped nails, preventing them from bouncing off the mount upon impact. Even so, the lunette suffered extensive damage and its fragments were strewn across the gallery floor (fig. 4). A systematic recording and retrieval system was employed to gather the fragments, which proved helpful in locating where the broken pieces belonged once the reassembly process began. The lunette was broken into pieces ranging in size from tiny glaze flakes to larger pieces weighing up to five pounds, all of which were riddled with cracks. Fortunately, major elements such as the head, hands, and even the little souls remained remarkably intact.fig. 3. The Saint Michael lunette set into a modern gilded frame, shortly after it was acquired by the Museum in 1960fig. 4. The lunette as it was found in the gallery on the morning of July 1, 2008TreatmentThe conservation treatment was lengthy but relatively straightforward. The first step was to sort through the debris to find all the glaze flakes and ceramic pieces, separating them from damaged mount components, including plaster and wooden shims. Plaster dust had infiltrated even the smallest cracks in the ceramic body. Thorough and careful vacuuming and surface cleaning prepared the pieces for the next step. Loose pieces contained within the frame after the fall were grouped according to where they were found on the object. Disassociated pieces that had flown across the floor had to be relocated by finding clues in the color and surface texture details to help put the puzzle back together; this step was painstaking and continued for months. Many internal fragments without glaze were set aside and not used because they were impossible to relocate. Furthermore, when fired clay breaks and is reassembled, the overall dimensions of an object can increase after bonding. If all the internal fragments had been used, the accumulation of such minute increases would have resulted in an imperfect alignment of Andrea’s sculpted, glazed surface.Several dry runs (assembling pieces without adhesive) were carried out to determine the correct sequence of assembly and to avoid lockouts (fig. 5). Pieces were bonded with a reversible acrylic resin and held together with clamps while the adhesive set, usually over a two-week period (fig. 6).7 Assembling a large section all at once was avoided, as the weight of the pieces could cause slippage and misalignment during the slow setting time. Such sections were done in several stages, adding a smaller group of bonded fragments to a larger piece, and so on, giving the adhesive time to fully set before bonding the next fragment group. It was crucial not to rush the process so as not to leave out any necessary pieces. Once the sections were assembled, then the multitude of glaze flakes could be placed and bonded. Such a three-dimensional puzzle was challenging, as the infinite variety of shapes and surfaces of the pieces demanded an assembly unique to each section. The characteristics of the clay pieces dictated how they interlocked, and assembly was carried out accordingly.fig. 5. Sorting and locating fragments of the lunettefig. 6. Bonding and clamping a section of the wingMissing areas were filled with reversible conservation materials, and inpainted with acrylic paints. The famous Della Robbia blue proved to be challenging to replicate due to a well-known but vexing characteristic of many modern blue pigments. The same blue pigment can appear to be quite a different hue depending on the color temperature of the ambient light source, a phenomenon described as “metameric shift.” However, we found that mixtures of Golden Acrylic’s ultramarine blue, Naples yellow, raw umber, and occasionally titanium white had less of a metameric shift than others and remained successfully color-matched to the original Della Robbia blue even under gallery lighting.8After assembly, we turned to creating a new mount for the object. The sections of the lunette were carefully designed to fit tightly together according to a specific sequence of assembly. Della Robbia clearly meant to hide the gaps between sections because, once the relief is assembled in this way, its joins are barely noticeable (fig. 7). To maintain this illusion, a new low-profile and unobtrusive mount was fabricated from a solid aluminum panel and custom-made brass clips to hold each section of the lunette securely. Finally, the visible portions of the clips were inpainted with acrylics to match the surrounding glaze color. When fully assembled, the lunette and its backing plate were secured to a reinforced wall with an interlocking cleat. Saint Michael the Archangel has now returned to the same gallery in which it was displayed before the accident.fig. 7. Diagram highlighting the twelve sections of the lunette. Numbers indicate necessary order of assembly. Once the figure was assembled, egg-and-dart could be placed in any order.Discoveries Made During TreatmentThe detachment of the lunette from its frame allowed us to study—for the first time in decades—the back and sides of the sculpture in great detail. Even more unusual was the opportunity to examine the interior clay structure of the fragments, providing us with a rare glimpse into the working methods and expertise of the Della Robbia workshop. The following describes some of the most informative details discovered during the conservation treatment.Tool Marks and ImpressionsIn 2013 at La Torre Ceramica d’Arte, a ceramic factory producing Della Robbia reproductions in Scandicci, Italy, one of the workers demonstrating the process of pressing clay into a mold explained, “Pressing the clay into the mold, I can feel the resistance of the plaster below and can therefore make the walls even.”9 This contemporary account bears a direct connection to our observations of the Saint Michael lunette. In sections like the torso, which is in high relief, a great deal of care was taken to press the clay into the mold evenly (fig. 8a,b). In contrast, the head was sculpted by hand as a solid form, then hollowed out to achieve even wall thickness and reduce mass. Generally speaking, consistent wall thickness is critical to avoid cracking and warping as an object is dried and fired. Throughout the lunette, each section that has areas of high relief was hollowed out from the back for this reason.fig. 8. (a) The torso section; (b) The torso from behind, showing even wall thicknessFigure 9a illustrates how the process of pressing clay into the mold left numerous finger marks. There is some discussion among scholars as to whether the clay was pressed into the mold or the mold filled completely and then scooped out. Examples supporting both strategies have been observed, but it is clear from these marks that the clay was quite wet when introduced into the mold.10 Occasionally, distinct impressions of finger-prints are preserved on unglazed surfaces (fig. 9b). A variety of tool marks is present along the sides of the lunette’s sections including incised graffiti, paddling marks, and impressions of wood planks pressed against the clay (fig. 10a, b). The marks not only provide a sense of the physical labor involved in forming, handling, and maneuvering large clay sculptures before they were fired, but also betray the direct touch of the workers—the immediacy of the malleable material responding to a proficient hand.fig. 9. (a) Finger marks from pressing soft clay into the mold; (b) Fingerprints found on the back of the lunettefig. 10. (a) Tool marks along the side of a section; (b) Wood impressions in the clayClay Body and GlazeLooking along the edges of each broken piece provided a cross-sectional view of the Della Robbia terracotta clay body itself. One of the most striking findings revealed how seemingly little care was taken while working the clay. On the right arm, for example, large voids and folds suggest that the wet clay was hastily pressed into the mold (fig. 11a). Distinct color variations and lumps observed in other pieces indicate that the clay was not thoroughly wedged before use (fig. 11b). As students of ceramics know, properly wedged, or kneaded, clay produces a compressed matrix with smooth consistency and even color. Wedging is done to reduce risk of firing flaws that can be caused by the rapid and destructive expansion of water vapor contained inside air pockets. It was surprising to discover that the Della Robbia workshop, known for reliably producing large-scale sculptures, was not meticulous in handling its clay. This ostensibly cavalier workmanship reveals that the workers had an intimate understanding of their clay and of how far the boundaries could be pushed while still achieving an excellent result.fig. 11. (a) Air pockets revealed in the clay body under Saint Michael’s right hand; (b) Lumps and color variations in the clay visible in a cross section of a large fragmentThe Della Robbia clay has been studied extensively. Legend persists of a secret source at a property they had along the Arno River. This chalky clay, also referred to as “marly clay,” fires to a pale buff color (as opposed to the usual terracotta red) and has the effect of making the overlying glazes appear especially luminous. It also fires well at a wide range of temperatures and is a good “fit” for the Della Robbia glazes, in that the clay and glaze expand and contract at the same rate throughout the firing.11 The Della Robbia family carefully guarded the secrets of their clay preparation as well as their glaze recipes, much to the chagrin of contemporary sculptors attempting to produce similarly glazed works.Glaze RepairsOne unexpected discovery made during the treatment concerns a large firing flaw in the torso section originating from the time of manufacture. When the lunette fell from the wall, a large section of the drapery broke away, exposing an area of the clay body (fig. 12a). Upon close examination, we found that the matching surfaces of the exposed “abdomen” and the detached fragment were not fractured; they were, in fact, smooth, and it was clear they had never been whole. This observation suggests that the torso was molded as a basic form and was then further sculpted by adding more clay to create the drapery with its many undercuts (fig. 12b) and other details such as the lion’s head pauldron on Saint Michael’s right shoulder. Probably in this case, the underlying clay was too dry to adhere to the supplementary layer, and as a result, they separated during the first firing.fig. 12. (a) “Abdomen” area exposed after drapery fragment detached; (b) Torso section with drapery fragments in place; the dotted red line indicates location of fragment seen in next figure; (c) White glaze on the underside of a portion of drapery fragment, revealed after accidentTo salvage the piece, Della Robbia applied white glaze to the exposed ceramic substrate and the drapery fragment was put back in place; some of this glaze is visible in figure 12c. A thicker paste of glaze and fired clay was used to fill gaps around the edges.12 Finally, the whole section was glazed in white and blue in the usual manner, and fired a second time during which the “glaze glue” melted and bonded the separated fragments together. In this example we see how the work shop’s proficiency with clay and ability to adapt to the unexpected enabled them to execute this potentially risky repair in order to save an extraordinary work. The glaze repair secured the fragment in place for more than 540 years until the impact of the recent fall caused it to detach. There is evidence that the Della Robbia workshop often executed glaze repairs, but to see it as we did on Saint Michael’s torso is rare.13DiscussionThe Della Robbia workshop was an industrious place. Apart from Saint Michael the Archangel and Prudence, many other works dating to about the same time have been attributed to Andrea, for example The Madonna of the Architects, as well as the Annunciation, which was the first of many commissions of large-scale altarpieces for the sanctuary church associated with Saint Francis of Assisi in La Verna.14 One might think that in such a prolific environment, attention to detail might lapse. However, despite the volume of work, the Saint Michael lunette is a result of carefully performed steps, starting with planning the composition and structure, and continuing through all stages of sculpting and glazing.Decisions on how to divide the work into sections so they fit together relatively invisibly were made early in the manufacturing process. For example, Michael’s left wing is divided into two vertical sections, but the gap between them is disguised by the high relief of his hand and sleeve. At that time, the sides of each section were modeled to slant inward, creating inverted V-shaped voids that would help secure them to the wall. The cavalier approach to wedging clay with the resulting folds and air pockets, the sweeping finger marks that cover every inch of the torso’s interior, and tool marks in the form of scraping, paddling, and cutting are all evidence of the workmen’s direct and expert engagement with the heavy clay. Glaze repairs indicate a commitment to saving a damaged piece and the subsequent adept use of the materials at hand to achieve a successful result. Errare humanum est is exemplified in one small triangle where blue was accidentally painted over white and fired turquoise—a tiny error in a sea of excellence. Above all, Saint Michael’s face carries a sublime and transcendent expression born from Andrea della Robbia’s genius. Here we see how the combination of artistic mastery with artisanal tradition produced a magnificent work.PrudenceThe Prudence tondo provides another opportunity to appreciate Andrea and the glorious consistency of his work at a time when the workshop was creating numerous commissions. One of the largest Della Robbia works at the Museum, the tondo depicts the cardinal virtue Prudence and, like Saint Michael the Archangel, is composed of multiple parts: seven sections for the inner tondo, and eight vibrant garland sections framing the piece, each containing hand-modeled and molded components. In a field of blue, a three-quarter-length young woman is portrayed floating among clouds, looking to her right. She holds a mirror in her right hand and, coiling vertically along her torso, a snake is gripped by her left. The surrounding garland is a colorful and realistic arrangement of citrons, oranges, grapes, quinces, cucumbers, and pinecones accompanied by their associated foliage, all grouped, and separated by blue ribbons.The figure of Prudence represents the mother of all virtues; she is morally good, the measure of justice, temperance, and fortitude. The snake represents wisdom and careful thought, and the mirror refers to the Delphic inscription “Know thyself.” One of Prudence’s most striking attributes is her second face—that of an old man—implying wisdom of the past. Prudence herself looks into the future.15Apart from documentation of the tondo’s modern provenance, there is little known of its origins in Italy.16 Most of the literature on Prudence has focused on attribution, wavering between Luca and Andrea. The relief was attributed to Luca until the 1980s when John Pope-Hennessy argued for Andrea based on stylistic details such as the posture of the figure, treatment of the garments, and the position of the eyelids.17 Prudence is closely associated with two other tondi depicting the virtues Temperance and Faith.18 However, details of the Faith tondo indicate that it may be from a separate decorative scheme depicting the theological virtues (Faith, Hope, and Charity). Art historical dating of Prudence to about 1475 appears to have been based on an association between its creation and the time when Andrea became the de facto leader of the workshop due to his uncle’s failing health.19After Prudence was purchased by the Museum in 1921, the tondo was displayed in the galleries for many years, but eventually it was placed in storage, where it stayed out of sight for a generation. The decision to conserve Prudence came in 2014, in preparation for Marietta Cambareri’s exhibition “Della Robbia: Sculpting with Color in Renaissance Florence,” which was notable for reframing these works as true sculpture rather than merely decorative arts.20TreatmentWhen conservators examined Prudence and associated archival images they found the tondo was relatively unchanged from when it was acquired by the Museum. On the front surface were aged and discolored restorations and extensive plaster fills (fig. 13a). The fifteen sections of the tondo were mortared into a heavy iron ring surrounding the relief, and on the back were the remains of a brick wall from a previous installation (fig. 13b).fig. 13. (a) Front of Prudence before treatment; (b) Back of tondo, showing remains of brick wallOur examinations determined that the tondo was too unstable to travel safely on loan, and we decided to completely disassemble it and create a new mount. The tondo was dismantled in a slow and deliberate process that took place over several months. With the sections separated, we turned to removing the remnants of its previous installation and cleaning away centuries’ worth of accumulated dirt. We also removed oil-based restoration paint that covered not only plaster fills, but also significant areas of perfectly preserved glaze. After cleaning, any losses were filled and inpainted as done with Saint Michael the Archangel.One of the