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Helping Artworks withstand Museums
08.02.2019, by
Wood is a living material. And this shows in paintings on wood, slowly cracking, bending and warping—the price to pay for being on public display under conditions that are often far from ideal. In 2018, a team of restorers and scientists from the LMGC set up a novel experimental system at the Musée Fabre in Montpellier (southern France). Their goal was to unlock the secrets of how wood changes over time and the impact of those changes on the artworks.
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Five hundred years ago it was brand new. Today a long crack stretches across the surface of “The Holy Trinity Crowning the Virgin.” The culprit behind this disfiguring scar: wood! The anonymous work was painted on four wooden panels whose movement is restricted by the frame and the painting’s backboard, both also made of wood.
Christophe HARGOUES / LMGC / CNRS Photothèque
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A technique called stereo image correlation is used to measure the warping of the wood. Small Japanese paper stickers are placed on the front and back surfaces of the painting. These markers serve as reference points for four cameras installed on both sides of the work and programmed to take a photograph every 30 minutes.
Christophe HARGOUES / LMGC / CNRS Photothèque
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In order to exert precise control over the ambient humidity, the painting is placed in a hygro-regulated environmental chamber. The researchers change the relative humidity by 10%, a rate high enough to study the warping phenomenon without damaging the artwork. A high-precision scale, seen here under the painting, allows them to measure the amount of water absorbed by the wood.
Christophe HARGOUES / LMGC / CNRS Photothèque
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Another device is attached directly to the back of the painting to take local measurements. Mounted two by two, metal rods detect every movement of the wood via highly-sensitive “deformometric” sensors. The latter are connected to continuous recording instruments in order to register even the slightest change in the panel.
Christophe HARGOUES / LMGC / CNRS Photothèque
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A wooden backboard that was added to consolidate the painting in the 1970s had the opposite effect: it actually caused more warping! Here a researcher measures the swelling of a sample from the support after fluctuating the humidity in the environmental chamber.
Christophe HARGOUES / LMGC / CNRS Photothèque
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The combined results of the different methods make it possible to observe the curvature of the wooden panel. This is a major step towards the restoration of the painting, and a milestone in the project, whose primary goal is to improve the preventive conservation of artworks.
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