In the process, conservators at the Los Angeles-based center are pioneering the use of digital X-ray radiography, near-infrared imaging, electron scanning microscopy and mass spectrometers to probe the painter's flamboyant work. Their forensic tools turned the $140 million canvas into a crime scene in which the culprit is the chemistry of decay.
"From the chemical composition and buildup of paints, we are unlocking evidence of Pollock's creative process, his choice of materials, and any alterations through time," said Getty conservation analyst Alan Phenix.
Mural is one of a half dozen Pollock paintings undergoing restoration recently at collections around the world. The University of Iowa, which owns it, commissioned its repair. Art collector Peggy Guggenheim, who commissioned Pollock to paint "Mural" for her New York townhouse, donated it to the university, located in Iowa City.
Photos: Probing Pollock's 'Mural'
Experts examined 'Mural,' by Jackson Pollock, at the Getty Conservation Institute in Los Angeles.
Graphic: The Restoration Work
Get an up-close look at some of the restoration work on the painting, see the results of analysis of the paint used, and take a look around the Getty Conservation Institute.
The massive 8-by-20-foot canvas was a turning point in modern art when it was painted in 1943, energizing the abstract expressionism movement. "Scholars have always looked at this painting as a seminal work; a moment in which Pollock is changing," said Yvonne Szafran, senior conservator of paintings at the J. Paul Getty Museum, which is collaborating on the project with the conservation institute at the Getty Center complex.
The 70-year-old painting embodies the conundrum posed by all famous works of art—whether conservators should restore and refurbish, or simply preserve what they find as best they can. But time is especially cruel to modern art. Commercial paints fade and flake. Canvas sags. Frames warp. Exotic creative materials, from synthetic dyes, neon tubes and plastics, to body fluids, animal parts and table scraps, readily disintegrate or rot.
That limits a conservator's choices in the effort to save modern works. "If they are made of lettuce, there is only so much you can do," said conservation expert Gillian McMillan at the Solomon R. Guggenheim Museum in New York.
And the artist's palette keeps expanding. "If a material has been invented—and there are millions of materials out there—I swear there is an artist who has tried to use it," said James Coddington, chief conservator at the Museum of Modern Art in New York, who has been restoring three Pollock paintings. "It is very hard to know what the longer-term performance of these materials might be."
Alan Phenix at the Getty Conservation Institute points to a digital image of the Jackson Pollock painting under repair.
The artist's signature.
At the Getty, researchers are trying to make necessary repairs without changing the character of Pollock's work—to preserve rather than restore. But the materials in his painting posed their own technical challenges. The painting is so large that it took three days to X-ray the canvas in its entirety.
"Big paintings like 'Mural' lead a hard life," said Getty conservator Laura Rivers. "They are stretched, un-stretched, rolled, unrolled over and over."
As a result, its paint in places has chipped. Some colors have faded—driven by the internal chemistry of the pigments they contain. The canvas itself has sagged under the weight of all the paint it holds. And like other famous works of art, Pollock's painting also suffered the ill effects of earlier preservation work.
Using a noxious solvent called xylene, Ms. Rivers spent weeks removing the acrylic varnish applied across the painting during a restoration in 1973, which had masked the painting's texture and sheen. To protect herself from the fumes, she wore a face mask as well as three layers of gloves.
To safely analyze the chemistry of Pollock's paints, the conservators used a series of noninvasive imaging techniques, including infrared imaging and X-ray fluoroscopy, which let them probe the canvas with different electromagnetic wavelengths without having to touch it. A single application of teal blue contained 12 different pigments, the spectroscopic analysis showed.
Microscopic examination of paint samples—each no more than a half-millimeter across—revealed as many as 25 layers of color splashed, spattered and brushed on the linen canvas.
Their tests revealed that Pollock had been surprisingly cautious for an artist once renowned as "Jack the Dripper" for his exuberant splatters of color. He painted "Mural" methodically, working from right to left, with the canvas upright and not horizontal on the floor, as with many of his later paintings.
Moreover, Pollock relied almost exclusively on traditional oil paints, the researchers determined. "In a funny way, despite its radical creative dimension, it is really quite conservative from a materials point of view," said Dr. Phenix.
But the tests also showed that Pollock had used a white, water-based house paint to lighten the background spaces between the swirls of oil paint. That paint had grown transparent as it aged. "Oil and water don't mix, so you get some odd interactions that pose a conservation challenge," said Dr. Phenix.
Even so, the Getty conservators don't plan to repaint those patches. "We accept changes like that," said Ms. Szafran. "It is part of the aging of the painting, its inherent vice."
In the weeks ahead, the Getty researchers expect to rebuild the wooden framework that supports the large canvas and keeps it taut. They have spent months consulting with art scholars on the proper way to proceed. "You are balancing historical accuracy and authenticity with what you know of the artist's intent," said Getty conservation scientist Tom Learner. "We want this painting to look like a well-preserved 70-year-old."
Write to Robert Lee Hotz at sciencejournal@wsj.com