The purpose of this work is to characterize Portuguese painting ground layers from the 15th and 16th centuries (1450–1600), focusing particularly on the Coimbra, Lisbon, and Viseu workshops. Calcium sulfate, used regularly in these layers is common in the Iberian Peninsula as a natural resource. Its use is now confirmed, as already studied in Spanish paintings, and it was prepared generally by addition of animal glue. Besides the common esthetic language to the various painting workshops at the time, chalk/calcite (calcium carbonate), gypsum (di‐hydrated calcium sulfate), and anhydrite (anhydrous calcium sulfate) ground layers have specificities that allow characterizing different compounds. The cross‐sections from a set of six groups of Portuguese paintings were examined by optical microscopy and micro‐confocal Raman and Raman spectroscopic mapping imaged the location of the different compounds in the cross‐section. Results were integrated with those obtained by micro‐X‐ray diffraction and scanning electron microscopy with energy dispersive X‐ray spectroscopy on the same samples. In most cases, the ground layers are made of calcium sulfate in the form of the so‐called gesso grosso (mainly anhydrite with small amounts of gypsum). Differently, the Viseu paintings have calcium carbonate ground layers. These results put in evidence differences between the examined groups giving important information on the various workshop practices and also on the possible future conservative intervention on the paintings. Copyright © 2014 John Wiley & Sons, Ltd.

The early 17th century mural paintings set from the low-choir of the extinct Dominican Convent of Nossa Senhora da Saudação in the town of Montemor-o-novo were analyzed by a setup comprising visible spectra-colorimetry and scanning electron microscopy coupled with energy dispersive X-ray spectrometry (SEM-EDS) complemented with optical microscopy (OM), micro X-ray diffraction, micro FTIR, and micro Raman spectroscopy. The main goals were material and diagnostic characterization of the paint layers and pictorial techniques used by Jose de Escovar workshop, one of the most active and controversial easel and mural painters of Evora Archiepiscopate between 1585 and 1622. The results show a differentiate use of red, blue, and green pigments in an alkaline environment. Stable mercury sulfide (HgS) was identified in almost all red areas in the latest scenes while, in the first ones, red ochre (Fe 2 O 3 ) is the predominant pigment. Faded smalt (a co-potassium silicate glass) is present pure in the sky background or mixed with red ochre in the garments at the beginning of the low-choir but less at the end. Five kinds of copper-based materials, with different degrees of color alteration, were found, namely malachite and azurite, copper chlorides, copper sulfates (e.g., posjnakite), and pseudomalachite. Another curious feature is the uneven use of a limewash made with slaked calcitic lime in the carnations. Lack of material, internal organization strategies, or technical differences within the team are probably the most likely causes.

This paper employs various techniques to analyze the mixture of chalk and binder materials used, by Portuguese and Flemish painters in the 15th and 16th centuries, to enhance the reflection of light in paintings.