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Microscopic Slivers of Artworks Reveal Hidden Truths | Conservation Lab

For art conservators, the inner geography of a painting speaks volumes.
Image de Une : Coupe transversale de : Franz Kline, Orange and Black Wall (1959), huile sur toile (169,5 x 367 cm). Cet échantillon montre que Kline faisait des expériences avec plusieurs types de bleu sur cette zone, avant de finir avec du blanc. Le mélange intriqué des couches du milieu dévoilent qu’il a appliqué une peinture plus sombre tandis que le bleu clair étant encore frais. Toutes les photos sont du Dr. Corina Rogge et sont publiées avec l’aimable autorisation du Museum of Fine Arts de Houston.

In art institutions across the globe, time machines and investigation rooms exist behind closed doors. Dusty artworks go in and come out looking centuries younger; artists’ secrets are brought to light; and hidden, unfinished images emerge from behind famous compositions. Every week, we'll peek beneath the microscope and zoom in on the art of preservation, where art meets science and just a little bit of magic: this is Conservation Lab.


A microscopic flake extracted from an oil painting may not seem like much to the naked eye, but 20 times magnified, it begins to look like a geologic cross section. Earlier colors emerge as stratified layers beneath the surface; speckled paint takes on the appearance of rock; and some bands of color appear to be in motion, sliding into one another like tectonic plates. In the eyes of the art conservator, the geography inside that half-a-millimeter speck is a rich mine of information.

Cross section from: Unknown Master, Spanish, Saint Peter (15th century), Oil and gold leaf on wood (147.9 x 54.3 cm). The cross section is illuminated with normal light at left, and ultraviolet light at right—the latter better highlights the presence of three different red pigments to achieve an illusion of depth.

According to Dr. Corina Rogge and Dr. Zahira Bomford at the Museum of Fine Arts, Houston, this kind of cross-sectional analysis was first described in 1914, and further developed in the 1930s by a conservation scientist working at the Fogg Art Museum at Harvard. While it’s possible to gather a few clues about the internal layers of a painting by looking inside a crack with a microscope, the extraction of a tiny sample is a much more direct method. It can be done on any painted or coated object—from sculptures, paintings, and works on paper, to furniture and photographs.

Cross section from: Franz Kline, American, Red Brass (1955), Oil on canvas (173.4 x 99.3 cm). The unusual appearance of this sample suggests there were cracks in the painting before the top green and yellow layers were applied, from stretching and unstretching the canvas, or bumping it in the studio, for example.

“Initially the paint samples were embedded in wax and then cut with a microtome,” explain Rogge, research scientist, and Bomford, senior conservator of paintings. Today, other mounting media, like polyesters and epoxies, are also used, and in order to create the smooth surface that is photographed, the sample is often polished rather than cut. “Any object is a possible candidate,” they point out, “but because we are engaging in a destructive process, we only take samples from areas of extant damage or loss. So we would not sample from a painting in perfect condition.” That said, given the size of the sample, which is pulled out with a fine needle or micro-chisel and “much tinier than the head of a pin,” the operation barely leaves a scar, if any at all.


Cross section from: Lygia Clark, Brazilian, Espaço modulado no. 2 (1958), Industrial paint on wood (89.9 x 29.8 cm). While this painting looks simple on the surface, “this sample, taken from a white area, shows a very complex stratigraphy of six different layers.” This could indicate that Clark kept editing her color choices, or was experimenting with paint textures.

Under the magnifying glass, the minuscule fragments answer all kinds of questions about the object’s history and the artist’s process. Did they work wet-on-wet, or allow a drying period between layers? How many layers are present, and are they all part of the artist’s original surface? Are there any transparent glazes modifying underlying colors? The color of the ground layer is often of crucial importance: Since many artists use colored grounds to achieve a specific tonality in their work, it can “help site a work in an artist’s oeuvre or general time period.”

Cross section from: John Vardy (attributed), English, Stool for the Palm Room, Spencer House, London (c. 1757), limewood, gilt, and upholstery (not original) (43.2 x 67.3 x 55.9 cm). The wood of this stool is now entirely gilt, but its past lives in other hues are revealed in the sample.

By amassing entire libraries of these samples, conservators, historians and scientists can begin comparing one cross section to another. This is where the dots really start to connect. “Little by little, across time, and across geography, researchers build up an understanding of the unique technical features of specific artists,” write the MFAH conservators, “which contributes to all kinds of problem-solving including aspects of authorship and authenticity, as well as a fuller appreciation of original technique and a deeper understanding of aging characteristics.”

As for us non-scientists, we can appreciate these abstract gems as artworks in their own right.

Stay tuned for the next Conservation Lab, which debuts every Tuesday, only on The Creators Project. 


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