The rose of the Sainte-Chapelle in Paris: sophisticated stained glasses for late medieval painters

The restoration of the rose (15th century) of the Sainte-Chapelle in Paris, France, offered a unique opportunity to investigate the color and chemical composition of these emblematic medieval French stained glasses with non-destructive analyses. The obtained results are aimed at complementing the knowledge from art historians and thus together trying to compensate for the total absence of archives on the construction of the rose. Comparison with the glasses of the nave (13th century) reveals an important evolution of the aesthetics based on new types of glasses: new colors and extensive use of flashed glass. The systematic study of the chemical composition of both sides of each glass piece revealed that about half of the studied glasses were flashed. For non-flashed glasses, this comparison allowed evaluating the influence of glass surface weathering, although very moderate, on the composition variability. In light of the variability criteria, the multivariate analysis of the chemical composition allowed inferring that most glasses originate from the same production glasshouse. The new colors result from the original composition of flashed glass, allowing superimposing otherwise incompatible redox states of the coloring transition elements. The comparison with the glasses of the nave reveals the glass technology evolution that occurred over two centuries and allowed the production of new glasses for the medieval glaziers at the eve of the Parisian Renaissance.