Analytical investigation of 14th century stained glass windows from Santa Croce Basilica in Florence

The Basilica di Santa Croce (Basilica of the Holy Cross) is the major Franciscan church in Florence (Italy). Among the prominent masterpieces preserved in this church, there are 22 medieval stained glass windows. Between 2000 and 2013, the Opera di Santa Croce started a restoration campaign of six of the most important ones, dated 14th c. In this paper, the archaeometric data collected during the restoration campaign are reported. Two major base glass compositions (potash-lime-silica and soda-lime-silica) were identified by quantitative chemical analysis. Results are compared with similar investigations on Italian stained glass windows of the 14th-15th centuries and many similarities are highlighted. Some interesting "secrets" of the coloring techniques based also on multilayer glass pieces were revealed. Finally, SEM-EDS analyses allowed the main weathering glass phenomena to be investigated.