Recovering Vanishing Images in Paintings

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On Wednesday, Feb. 8, Jennifer Mass, senior scientist and head of the Scientific Research and Analysis Laboratory at Winterthur Museum in Delaware, presented her lecture entitled, “When masterpieces meet x-rays: Recovering hidden and vanishing images in paintings” as part of this semester’s Natural Science and Mathematics (NS&M) Colloquium. Mass discussed how x-rays can be used to reveal why a painting is degrading and if the painting has been altered in any way.

“There are only about a hundred or so chemists in the U.S. who spend their careers on the scientific study of objects of art,” began Mass. This type of scientific study is important because it can prove the authenticity of a piece of art, which is invaluable information to people purchasing expensive paintings.

The scientific study of art can also reveal what art conservationists have done to a painting over the years. According to Mass, “20 percent of what you’re looking at [in a painting] is material that’s been added by art restorers and conservators.” Only recently have people begun taking extensive notes on what kinds of things were done in prior and more current restorations.

Modern science has changed the way art conservationists work with damaged pieces of art. For example, Mass explained that in the nineteenth century, plaster was used to retain ceramics. However, it is now understood that the sulfates in plaster can cause further damage to a ceramic piece of art as opposed to retaining it.

The science of using x-rays to study how a piece of art is interacting with its environment is very important because x-rays are non-destructive. This just means that in order to do an x-ray, one does not need to remove a sample from a piece of art, thus avoiding permanently damaging a small part of it.

One painting that Mass has done a lot of work with is Matisse’s “La Bonheur de Vivre” (The Joy of Life), which was painted in the winter of 1905 to 1906. “Matisse had very little money for artist materials,” said Mass. “He used very inexpensive paints.” Because of this low quality paint, a lot of flaking and major color changes have occurred. For instance, the warm yellow color of some foliage in the painting now appears a dull tan color.

By using different kinds of x-rays, Mass and other scientists were able to discover the composition of the paint in Matisse’s art. There are high concentrations of cadmium, lead, and zinc. Cadmium is the chemical in the yellow pigment that faded. Paint continues to react to its environment even after it has finished drying. “It is continually reacting and undergoing hydrolysis,” said Mass.

One of Mass’s most significant discoveries has been through the technique of confocal x-ray fluorescence (XRF) microscopy. This kind of x-ray produces a three-dimenstional map of paint layers. “It gets information about all the paint layers individually, instead of all the paint layers simultaneously,” said Mass. A traditional x-ray provides data about all chemicals present in a section of art, while a confocal x-rays provides the series of changes in chemical composition occurring as the x-ray travels through the different layers of paint sequentially.

Using confocal XRF microscopy, Mass was able to reproduce a 1918 full-color painting buried beneath a family portrait painted by N.C. Wyeth in the 1920s. “XRF intensity mapping can be used to digitally reproduce a buried painting,” said Mass. “It allowed us to identify the chemistry… of the buried painting.” This technique can also be used to see if an artist painted over anything while creating a painting or made any changes in the position of objects or subjects in the piece of art. Another technique discovered in the 1960s, infrared reflectography, can show an artist’s sketches underneath the polished surface of a painting.

Next week’s NS&M, on Wednesday, Feb. 15 at 4:40 p.m. in Schaefer 106, will be about the physiology of birdsong from UMBC’s Bernard Lohr.

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