14th-Century Stained-Glass Production for the Transept Chapels of Santa Croce in Florence, Italy: Collaboration and Workshop Practice

Stained-glass is marvelously luminous, inherently fragile, and one of the least accessible of all artistic mediums. These qualities--luminosity, fragility, and inaccessibility--hamper on-site analysis, further complicated by restoration, corrosion, and limited direct access to the recto and verso, not to mention candle soot and, particular to Florentine windows, impaired legibility due to a widespread, undocumented use of cold paint that has blackened over time. Transmitted light obliterates tiny glaziers' marks and idiosyncrasies in painting technique. All of these factors have impeded research on the design and production of the stainedglass windows that were fabricated to embellish the earliest family chapels constructed in the transept of the Franciscan Basilica of Santa Croce in Florence during the first three decades of the 14th century. However, an extraordinary research opportunity occurred when in 2018 the stained-glass window in the Bardi Chapel - attributed to Jacopo del Casentino and dated 1321-1330 - was dismounted for conservation by the Opera di Santa Croce, which facilitated a collaborative, interdisciplinary research project including Americo Corallini and Valeria Bertuzzi (conservators, Studio Fenice), the late Susanna Bracci and Giovanni Bartolozzi (chemists, Institute for the Conservation and Valorization of Cultural HeritageICVBC-CNR and Institute for Applied Physics-IFAC.CNR), and Renée K. Burnam (art historian, Corpus Vitrearum,United States and Italy). The window attributed to Jacopo del Casentino, originally glazed for the Velluti chapel and sheltered by a bell tower until it was moved to the Bardi Chapel in 1958, is in exceptional condition. The well-preserved glass reveals elements not before verified in Florentine stained glass nor mentioned in 14th-century stained-glass treatises. The study benefits from a body of data gleaned from recent glass restorations in Santa Croce and expands an understanding of stained-glass workshop practices in 14th-century Florence. The project contributes to the ongoing development of a "catalogue" of data, such as maker's marks and the chemical composition of particular glasses, instrumental for making connections, defining artists and glaziers, and identifying workshops.