During restoration work on one of Pablo Picasso's abstract paintings, conservators at the Art Institute of Chicago shed light on a hidden drawing by the Spanish artist.

Still Life, dated February 4, 1922, had localized areas of wrinkling caused by Picasso’s use of multiple paint layers with different drying rates. To aid treatment, the conservators carried out infrared and X-ray imaging of the artwork, but to their surprise the canvas told another story beneath the striking cubist one seen today.

"X-ray and infrared imaging, as well as cross-sectional paint analysis, revealed details about the design and level of completion of the first still life and clarified that it was indeed painted on the front of the canvas, then covered with a layer of white paint before Picasso painted the linear cubist still life," Allison Langley, head of Paintings Conservation, told IFLScience.

The revealed neo-classical still life (oriented at 90 degrees to the final image) depicted a pitcher, a mug, a rectangular object (possibly a newspaper), and another circular form obscured by the vertical crossbar at the back of the canvas, according to Langley and her co-authors in their study published in SN Applied Sciences. They added that “the scene was set up on a tabletop, or possibly a flat surface balanced on the seat of a chair.”

As the paint-drawn scene had soaked through the canvas, the transmitted rays could pick up on the hidden image despite Picasso’s efforts to completely cover this work with a thick, white ground layer applied using broad, loose brushwork. As Langley notes, this was an unusual move for Picasso.

"Picasso often reused canvases and this has been documented on works at the Art Institute and elsewhere," Langley said. "What is surprising is that he blocked out the first composition with a layer of white paint. This is unusual in his practice, as he typically painted directly on top of the earlier paint layers, often retaining vestiges of the original forms or colors in the final painting."

In the case of the 1922 Still Life, no evidence of the earlier composition could be seen on the surface – only the probing power of light could uncover this secret. Yet conservators are still in the dark as to why Picasso made this radical decision.

"During 1921 and 1922 he was working in two contrasting styles simultaneously, creating a series of linear cubist still lifes while also painting neo-classical figures and still lifes," Langley explained. "Perhaps he could not find a playful or artistic alignment of the curvilinear forms of the first still life and the hard edges of the final linear abstract composition in this instance."

Langley and her team also succeeded in their initial plan to help find new ways to conserve the final painting, which had been given to the art institute in 1953 by Alice B. Toklas – the partner of Gertrude Stein, a friend and collector of Picasso, and original owner of the artwork. Imaging revealed previous restoration attempts, which the team cleared out and reapplied, as well as securing localized areas from further flaking.

“The conservation treatment secured these fragile areas and revealed variations in surface sheen and paint application previously obscured by layers of grime, varnish, and discolored overpaint,” Langley and her co-authors concluded.