Mar 29 2011
The characterization of the porosity of ground layers in easel paintings: a first step towards understanding its role in water uptake, reactivity and material transport in 19th and early 20th century paintings.
The Swiss Institute for Art Research (SIK-ISEA) is studying the studio practice of Swiss painters of the late 19th early 20th century, the materials they used for their paintings, and the deterioration processes the paintings undergo as they age. Amongst other issues this study is looking at the paintings' grounds, which are mixtures of binding media, fillers, and pigments applied to a suitable support as a preparation for painting. In particular it has set a focus on the possible connection between the porosity of grounds, their absorption characteristics, the overall appearance, and the stability of the paintings.
Many different recipes for the preparation of lean and relatively absorbent grounds can be found in technical sources written since the late 17th century. There are a number of reasons why most artists preferred them: They soak up some of the binding medium of the paint, thus shortening its drying process and resulting in a good adhesion between ground and paint. From the end of the 19th century onwards, the fact that absorbent grounds lead to brightly coloured and matte picture surfaces was very much appreciated by painters that had ceased to work in the academic style.
In attempting to characterise the degree of porosity or the capability of a ground to incorporate moisture, the study addresses a pressing conservation question: The presence of an absorbing layer within the painting build-up has important consequences for the painting's stability. Issues of water-accelerated reactivity and moisture gradient-assisted material mobility within complex paint systems have been recognised but never studied. The characterisation of the structure of absorbent ground layers is a first step towards the study of the mobility of materials between layers.
Recent research at the Art technology department of SIK-ISEA in collaboration with TOMCAT beamline at PSI Villigen has shown that X-ray tomography is a uniquely powerful method to study the internal structure in intact ground samples. The current research challenge is twofold and lies in (i) estimating precisely the distribution of voids and pores and the connectivity of the porosity network at a micrometer scale, and (ii) visualizing the impregnation and transport of moisture through the ground. The 3D tomographic data sets are being studied using the Avizo software, which enables visualization and quantitative analysis of the data sets by providing appropriate filtering algorithms and advanced segmentation tools.