The Brooklyn Museum Conservation Department is dedicated to the preservation of every artwork in the Museum’s encyclopedic collection. The decision of whether or not a painting should receive conservation treatment depends on the condition and stability of the artwork. Before considering the most appropriate treatment procedure for a painting, art conservators often use historical records and scientific analysis to investigate the materials and working methods used by the artist. The better a conservator understands each layer within the painting, the better the conservator will be at developing possible treatment options.
Cross-section microscopy is a common analytical method used to investigate the many layers and materials used to create a painting. Although these samples are about the size of the period at the end of this sentence, they can hold a lot of important information.
First a tiny sample is taken under a stereomicroscope with the aid of a micro scalpel. These samples are then imbedded in an acrylic resin cube. The cube is sanded down and polished, cutting through the sample to create a cross-section of the paint layers.
Art conservators then examine the polished cross-sections using a polarized light microscope which can magnify the sample hundreds of times and is equipped with different light sources including transmitted, incident, polarized and ultraviolet light.
A comparison of visible light and ultraviolet light cross-section images helped conservators at the Brooklyn Museum to distinguish and classify the different layers in Édouard Vuillard’s 1897 painting, Portrait of Thadée Natanson:
These cross-section images show that the artist first prepared his (1) wood pulp board support with a layer of (2) clear size (probably protein-based like rabbit skin glue) before applying his (3) paint layers. The UV light allows us to see the bright fluorescence of a (4) thin varnish layer over top these paint layers, likely a natural resin such as dammar or mastic.
