[LUM#11] At the heart of a work of art

[LUM Magazine] - Published on December 20, 2019 in Heritage, Science-Society

Humidity, temperature fluctuations, the passage of time... in museums, paintings on wooden supports are put to the test. To better understand the movements of wood and thus better preserve these works, Delphine Jullien, a researcher at the Laboratory of Mechanics and Civil Engineering (LMGC), has designed a very special display case installed at the Fabre Museum.

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As evidence of a sometimes distant past, works of art have endured for centuries but have not been spared by the passage of time. Paintings on wood, for example, are subject to the natural deformation of this material, which can sometimes alter the works. To better preserve this heritage, conservators call on researchers, particularly the wood team at the Montpellier Laboratory of Mechanics and Civil Engineering (LMGC), which has solid expertise in this field, having already worked on the famous Mona Lisa in collaboration with the PPRIME Institute in Poitiers and GESAAF at the University of Florence (Italy).

This time, these researchers are examining The Holy Trinity Crowning the Virgin, a work exhibited at the Fabre Museum in Montpellier. "It is a^15th-century painting on a set of four oak panels, fitted with a frame and parquetry on the back," explains Delphine Jullien. "This prevents the wood from moving due to variations in humidity in the environment, which has led to the appearance of cracks that alter the paint layer."

To better understand how wood behaves, the researcher and her team set up a real laboratory in the heart of the museum, in full view of the public. "The painting is placed in a climate-controlled display case where it is subjected to humidity variations ranging from 53 to 63% relative humidity."

A high-precision scale measures the variation in the panel's weight and calculates the amount of water absorbed by the wood. A system of cameras that reconstructs the work in three dimensions and sensors known as "deformometers" continuously measure the movements of the wood and the deformations of the panel.

"This data will enable us to quantify and better understand the movements of a painting on wood, and thus work with restorers to propose solutions for better conservation," emphasizes Delphine Jullien.