Last month, I led a handful of members of the IMA’s Second Century Society through a special behind-the-scenes workshop in my laboratory exploring the practice of cross-section sampling in conservation science. A cross-section is a miniscule sample cut from an artwork so as to contain all the layers of the painting – from the topmost varnish to the lowest preparation layer. When examined under a microscope or probed using micro-analytical techniques, a cross-section tells the story of the artwork’s inception, creation, and aesthetic techniques in a way that no other analysis or connoisseurship can. Although the collection and preparation of these samples can take days, we whisked participants through the many steps of sampling, mounting, and analysis of a cross-section using materials prepared in advance – much like a cooking show – in order to explain this invaluable technique for understanding and interpreting artworks in the collection.
Recently, we installed Roy Lichtenstein’s Five Brushstrokes on the Sutphin Mall. The extraordinary process of carefully positioning and stacking these monumental artworks – one that involved cranes, work crews, and conservators – was captured on time-lapse photography. The morning after the installation, I found a plastic baggie with two small paint samples on my desk. As I turned the chips over in my hand, it was obvious they told a story of the sculpture’s creation – so I prepared a cross-section to check it out.
The five components of Brushstrokes are made of painted aluminum. One of the samples came from the horizontal red and white brushstroke (Figure 1), and it is obvious from the cross-section (Figure 2) that the white highlights were painted first and then the sculpture was masked off to add the red passages – you see the red layer over top of the white in the cross-section meaning that the red paint had to be the last to be applied. But what is all that thick pink stuff below? An industrial product similar to Bondo! Yes, it is an epoxy version of a fairing compound like that used in bodyshops to level dents and scrapes on your car. When an aluminum sculpture is fabricated, the surface isn’t always smooth, and so an epoxy or polyester filler is troweled on top and sanded smooth to give an even surface that is then painted.
This layered structure seems complex, but cross-sections can get much more interesting! Check out this cross-section from a wooden shutter salvaged from a historic property on the Dupont’s Winterthur Estate, Figure 3. Because the building was regularly repainted, the section shows over a dozen different paint schemes. Furthermore, irradiating your sample with ultraviolet light and imaging the visible fluorescence from the paints can help to identify additional layers in what looks like a single, thick white paint coat toward the bottom of the section – the shutter has obviously been touched up with the same color a few times too!
Cross-section sampling is, by its nature, a destructive technique since a small sample of paint must be sacrificed. However, these samples can be vanishingly small, oftentimes less than the width of a hair, and yet they yield an enormous amount of information about the materials, craftsmanship, and condition of an artwork.