Ana Isabel Seruya

Characterization of glue sizing under calcium carbonate ground layers in Flemish and Luso-Flemish painting – analysis by SEM-EDS, μ-XRD and μ-Raman spectroscopy

This work regards the study of painting techniques in Portuguese workshops of the 15th and early 16th centuries, specifically addressing the methodology used on the preparation of ground layers. The influence of Flemish painting in Portugal is evident in stylistic and iconographic themes of that period. As regards the painting materials, we confirmed that this influence also extended to the ground layer technique. The use of a sizing layer with calcium sulphate or garlic to isolate the support from the calcium carbonate layer was verified by SEM-EDS but not confirmed by μ-XRD or μ-Raman spectroscopy. This work is part of a larger project, “The invisible ground layer and its influence in Portuguese paintings from the 15th and 16th centuries: a question to be settled”.

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.

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.

GREGÓRIO LOPES painting workshop: characterization by X-ray based techniques. Analysis by EDXRF, μ-XRD and SEM-EDS

Gregorio Lopes is one of the most famous Portuguese painters of the 15th–16th centuries. This work is a contribution to the study of his painting technique, specifically addressing the methodology used in the preparation of ground layers, which has never been carried out previously with this multianalytical method. For this purpose characterization of the ground layers of a selection of his paintings was carried out by micro-Energy Dispersive X-ray Fluorescence spectroscopy (μ-EDXRF), micro-X-ray Diffraction (μ-XRD), Scanning Electron Microscopy - Energy Dispersive Spectroscopy (SEM-EDS) and complemented by micro-Raman spectroscopy. This work presents the results obtained on two altarpieces (c.1544) produced at the same period by this Portuguese artist. Ground layers are composed mainly of calcium sulfate — anhydrite and gypsum — and other compounds such as dolomite. Reference samples were prepared to obtain diffraction pattern of different percentage of gypsum and anhydrite and compared with the results from historical samples.

The 1685 blue smalt coating of the Coimbra Old Cathedral main altarpiece under scrutiny

Although smalt was used as an important pigment in European oil painting during the 16th and 17th century, records of its use in a monumental tridimensional artwork and even more in a tempera coating remain quite scarce. The main altarpiece of the Coimbra Old Cathedral is an interesting case study to shed light on the use of smalt and the trade practices of painters at the baroque period, in Portugal. The primitive colour scheme of this artwork of a Flamboyant style, achieved in 1502, was renovated during three subsequent interventions [1]. According to a historical record [2], a new polychromy was to be undertaken in 1685 by the local painter Manoel da Costa Pereira. Smalt pigment bound in oil was to be applied to the original blue surfaces, then ‘burnished’ to produce a polished smalt coating. A later restoration carried out in 1900 actually prevents from seeing what lies underneath. Several micro-samples were collected in the blue background and niches of the altarpiece. They were examined by optical microscopy (MO), Scanning electron microscopy (SEM) with energy dispersive X-ray Spectroscopy (EDS) and a staining protocol, to verify if the aforesaid pigment has effectively been used and if a drying oil has been employed as binder and a mean to obtain a high reflective blue surface. All the samples cross-sections observed by OM unveiled the 1685 blue coating, always containing several grades of smalt mixed together given their more or less intense hue for grains of similar size (Figs.1-2). SEM imaging put in evidence the conchoidal fractures of the particles, specific to the blue cobalt-containing potash glass and its processing by pouring the glass paste into cold water where it disintegrated into particles for its further use as a pigment [3]. SEM-EDS analyses performed on individual grains allowed the systematic detection of Si, K, Co, Fe and As, and sometimes traces of Ca and Al, except for St. Luke’s niche where Co was hardly found. The Co contents (about 3-4 wt%) are the expected ones, irrespective of the blue particles intensity [4-5], but its average of 1 w% in St. Luke’s niche may be related to a deliberate choice by the artist to apply there a paler pigment. Ni was sometimes detected within the grains. Its presence may point the use of smaltite, [Co, Ni]As3-2, member of the cobalt iron nickel arsenide minerals sourced from Saxonia, or erytrite ([Co,Ni]3[AsO4]2.8(H2O)), but its absence may also point the use of cobaltite, (Co, Fe)AsS, sourced from Sweden [3,6], therefore indicating the use of marketed products of at least two origins. The very low As content, varying between 2.2 wt% (Virgin background) and 0.9 wt% (St. Luke and Paul’s niches) suggests the cobalt ore was calcined so as to eliminate volatile compounds such as arsenic. Although the transparent particles of smalt were coarsely ground (the largest one measuring the impressive 64 μm across) to overcome their low hiding power, an unexpected result came out by OM and SEM-EDS giving evidence of the use of lead-based light blue and pink underlayers (Figs. 1-2) to give the final blue smalt coating more intense and subtle shades. Micro-chemical analyses carried out on cross-sections with a staining protocol (acid fuchsin and rhodamine B dyes) showed confusing results regarding the binder. It seems that smalt was bound with a proteinaceous substance stained red by acid fuchsin, such as parchment or animal glue, likely to prevent the pigment from being altered by the yellowing of a drying oil. The gelatinous nature of the binding medium kept the particles clearly suspended until the paint became dry. A final oil film might have been soon applied 158 doi:10.1017/S1431927614014494 Microsc. Microanal. 21 (Suppl 6), 2015