Assessing the decorative techniques of two Art Nouveau glass windows by optical coherence tomography (OCT)

This work presents an assessment of the different decoration techniques applied in the two glass windows from the Casa-Museu Dr. Anastácio Gonçalves (Lisbon, Portugal) by Optical coherence tomography (OCT). The Dining Room glass window was found to be decorated with grisailles and acid etching, and the Atelier window with grisaille, enamel, and cold painting. The alteration state of the surface decorations was also assessed. The thicker surface decorations (grisailles and enamels) presented cracks and detachments, in contrast to the thinner lines which are normally well preserved. OCT is a suitable technique for characterizing glass decoration in situ without dismounting the stained-glass window; and able to reveal the condition and methods of manufacture that cannot be detected simply by visual inspection.