Matisse: Radical Invention, 1913–1917

The Art Institute of Chicago Until 20 June

In 1913 the French artist Henri Matisse embarked on a period of restless experimentation, eschewing the rich colours and sinuous lines of his earlier works for a more abstract, geometric approach to painting, dominated by blacks and greys. He reworked his paintings again and again, scraping at the paint as if it were plaster and carving it like wax. An exhibition running until June at the Art Institute of Chicago, Illinois, analyses the evolution of these artworks using scientific methods to 'digitally peel away' many stages of the artist's compositions.

Matisse: Radical Invention includes more than 125 paintings, sculptures and drawings. It highlights two that the artist considered among his most pivotal: Bathers by a River (pictured, bottom right) and the series of bronze bas-reliefs titled Back (1–4). Bathers, which he painted in stages from 1909 to 1917, began as a pastoral scene depicting five nude women beside a waterfall. Matisse later removed one of the figures and transformed the others into sombre, abstract forms, isolating each one against columns of green, black, white and grey-blue, and turning a blue stream into a black band. To show how Matisse altered the painting over time, conservators at the institute combined various digital images of the work produced from infrared reflectograms, scanned X-radiographs and early photographs.

Photos of Henri Matisse with his canvas were assembled into a composite image (top right) and overlaid with X-ray images (bottom left) to reveal hidden details in Bathers by a River. Credit: TOP (L): A. L. COBURN, GEORGE EASTMAN HOUSE INTL MUS. PHOTOGRAPHY AND FILM. TOP (R) AND BOTTOM (L): R. G. ERDMANN/UNIV. ARIZONA. BOTTOM RIGHT: H. MATISSE, BATHERS BY A RIVER, THE ART INSTITUTE OF CHICAGO, CHARLES H. AND MARY F. S. WORCESTER COLLECTION, SUCCESSION H. MATISSE/ARS, NEW YORK.

Insights into Matisse's working methods show how science can transform our understanding of art.

X-rays reveal paint layers of different thicknesses and pigments of different atomic weight. X-raying of the nearly four-metre-wide Bathers canvas in the 1970s generated 122 separate X-ray films, or tiles. But pasting these together left gaps and distortions due to misalignments of the scanning beam. Using custom software created by mathematician Robert Erdmann of the University of Arizona in Tucson, the conservators have adjusted for these distortions and matched the separate tiles seamlessly. “It was only in the distortion-free image that we were able to pick out certain subtle details, such as the diagonal edges of the riverbank that are part of the earliest painted state,” explains conservator Kristin Lister.

In producing the infrared reflectograms, light of wavelengths between 750 and 3,000 nanometres penetrates the upper layers of paint to reach lower layers that contain infrared-absorbing media, such as charcoal, revealing sketches that are normally hidden below the surface.

The team also analysed historical photographs of Matisse taken while he was painting Bathers. In these, the painting is in the background at an oblique angle, partially obscured by the artist (pictured, top left). Erdmann wrote software to infer the positions and orientations of the camera relative to the painting in each of these photographs, and then reconstructed an image of the painting as seen from the front (pictured, top right). Conservators then overlaid the X-ray images (pictured, bottom left) and infrared reflectograms with composites of the historical photographs, allowing them to see which details Matisse had hidden and which he had not: for example, pink bodies from an early state of the painting were later partly encased with grey.

Laser-imaging technology has also revealed information about Backs, a series of four monumental bronzes of female nudes, sculpted between 1909 and 1930. Matisse fashioned each new Back from a plaster cast of the previous one, adding or removing plaster to gradually transform the curving naturalism of the first Back into a more simplified, stocky form. Three-dimensional digital models created by bouncing points of laser light off bronze casts of Back (I) and Back (II) demonstrate how Matisse modified the reliefs.

These fresh insights into Matisse's working methods show how science can transform our understanding of art. “Working with the conservators at the Art Institute of Chicago has been a wonderful experience,” says Erdmann, who usually generates computer simulations of fluid dynamics and analyses the microstructure of materials. He hopes that the exhibition will stimulate further collaborations applying advanced image analysis to art conservation.