Microscopy and X-ray spectroscopy analyses for assessment of gilding and silvering techniques of Portuguese illuminated manuscripts.

The objects of this study are various local charters (cartas de foral, in Portuguese) granted by Dom Manuel I, King of Portugal (1495-1521), which substituted for medieval ones and were intended to achieve an administrative unification. These are luxuriously illuminated manuscripts, and our study aims at obtaining a better understanding of the gilding and silvering techniques applied to the parchments, in which the forais were written, between 1500 and 1520. The combined use of microscopy and X-ray spectroscopy analyses allowed us to identify the vestigial materials used for making the parchments, including products such as salt (NaCl), lime (CaO), pumice stone (SiO2+Al2O3), and chalk (CaCO3). Chalk was employed as a whitening agent to give the parchment its final color and opacity. Shell-gold and shell-silver mixed in with animal glue or gum binding media were directly applied on type 1 and 3 forais, while very thin gold leaves (<1 µm) were applied over lead-based tempera grounds (50-180 µm thick) in type 2 forais. Silver was always employed in its finest form without a further protective layer (thus its recursive state of corrosion), while gold was used in various alloy grades.

Characterization of glue sizing layers in Portuguese wood paintings from the 15th and 16th centuries by SEM secondary electron images and µ-FTIR.

According to treatises on 15th and 16th century paintings, artists dedicated particular attention to the sizing layer-consisting mainly of animal glue applied onto the wood support before further application of the ground layer. The stability of a painting mainly depends on the presence of a very cohesive sizing layer. However, the study of these layers has not received special attention from researchers. In this article we present a methodology for characterization of the sizing layer both chemically, by IR spectroscopy (Fourier transform infrared spectroscopy), and morphologically, by scanning electron microscopy (SEM). Secondary electron images obtained by SEM allow precise characterization of such layers. Painting reconstructions were used as references in development of the method to study the sizing layer in real painting samples. Presented herein are examples of this study on 15th and 16th century Portuguese paintings, particularly on the Triptych of S. Simão, from the Aveiro Museum, and S. Pedro, belonging to the Mercy of Tavira.