Art and politics don't generally mix. Just ask Spanish painter Francisco Goya. Okay, you can't ask him directly, because Goya died nearly 200 years ago, but new x-ray analysis of one of his most famous paintings may shed light on the unique circumstances under which Goya painted it. It's the next best thing to asking Goya directly.

Via io9, I learned of a new technique called scanning macro x-ray fluorescence spectroscopy developed by researchers at the University of Antwerp and the Delft University of Technology. At the behest of the Netherlands' Rijksmuseum, they used it to analyze Goya's "Portrait of Don Ramon Satue," an 1823 canvas depicting a man who was then a judge in Madrid -- and a pal of the artist. And lo and behold, underneath the portrait is another, half-finished portrait of a French general. For some reason, Goya decided to paint over it.

It's admittedly speculative why he chose to do so, but the theory is that the under-painting dates back to between 1809 and 1813, when Napoleon Bonaparte's brother, Joseph, ruled Spain after Bonaparte ousted the Spanish monarchy. But then King Ferdinand VIII managed to take back his throne. This put Goya in an awkward position, as the Dutch scientists explained:

From the scans it can clearly be seen that Goya (1746-1828) painted his portrait of the casually-posed Spanish judge, Ramón Satué, over a much more formal portrait of a man wearing uniform. The decorations embellishing the uniform are those of the highest ranks of a chivalric order instituted by Joseph Bonaparte when his brother, the emperor Napoleon, created him King of Spain. The hidden portrait must thus date from between 1809 and 1813. Goya's portrait of Satué is signed and dated 1823.

Although the hidden sitter's face is not entirely legible, the portrait almost certainly depicts one of the French generals who accompanied Joseph to Madrid, and may, perhaps, even be of Joseph himself. The portrait is likely to have been left on Goya's hands when the French army was driven from Spain in 1813, and Ferdinand VII restored to the throne. Ten years later Goya would have had good reason to cover it up. He had subscribed to the liberal Spanish Constitution of 1820, and when Ferdinand resumed absolutist rule in 1823 Goya feared reprisals, going so far as to go into hiding with a kinsman of Satué's. Under the circumstances, his possession of a portrait of a Napoleonic officer could only have been construed as compromising.

This is not the first time unusual imaging techniques from the world of science have been brought to bear on the world of art. Back in 2008, I wrote about a team of European scientists who used synchrotron radiation to reconstruct the portrait of a peasant woman painted by Vincent van Gogh that the artist had then painted over when he created 1887's "Patch of Grass." It lay there, dormant, for 121 years until we finally had the technology to nondestructively analyze the painting and reproduce the hidden image, courtesy of the Deutches Elektronen-Synchrotron (mercifully known by the acronym DESY) in Hamburg, Germany.

Synchrotron radiation is a bit different from conventional x-rays; it's a thin beam of very high-intensity x-rays generated within a particle accelerator. The Cliff's Notes version of how it works is this: You fire electrons into a linear accelerator (linac), boost their speeds in a small synchrotron and inject them into a storage ring, where they zoom through at near-light-speed. A series of magnets bend and focus the electrons, and in the process, they give off x-rays, which can then be focused down beamlines. This is useful for imaging purposes, and for analyzing structure, because in general, the shorter the wavelength used (and the higher the energy of the light), the finer the details one can image and/or analyze.

Someone had already used conventional x-rays to reveal the rough outlines of the underlying portrait, but that technique just wasn't sufficient to distinguish between the many layers of paint. Also, pigments made from heavy metals tended to obscure the colors derived from other elements, resulting in what Joris Dik, a materials scientist and art historian at the Technical University of Delft in the Netherlands, described as "a very partial, fragmentary, color-blind view."

Dik and his colleagues took "Patch of Grass" to DESY and exposed the painting to the x-ray beams. The radiation excited the atoms on the canvas, which then emitted x-rays of their own, picked up a fluorescence detector. Each element in the painting had its own x-ray signature, so they were able to identify the distribution of metals in the many layers of paint, construct a 3D model, and then peel off the layers one by one in the virtual image until what lay beneath was finally revealed.

Per the Los Angeles Times: "The top layer consisted of paints made with zinc, barium, sulfur, and other elements. Behind that they found a uniform distribution of lead, which was used as a primer to hide the portrait and prepare the canvas for a new painting. Once that was removed, they combined the distributions of two more elements -- mercury and antimony -- to produce the outlines of the hidden portrait."

They found the remains of a portrait of a woman bearing a striking resemblance to the model van Gogh used while composing his famous "The Potato Eaters" in 1885, and used computer software to recreate the painting using their own version of a "paint-by-numbers" technique. Van Gogh, apparently, was known to recycle his canvases, which was quite thrifty and environmentally correct of him. Clearly, a man ahead of his time. In fact, some art experts think that as many as one-third of his earlier paintings have older ones underneath them.

Synchrotron light is a burgeoning research area, finding use in physics, chemistry, materials science, medicine, geological and environmental science, structural genomics, and (as we have seen) archaeology. The Diamond synchrotron in Oxfordshire is part of a growing number of world-class research facilities in that area. In fact, scientists from the University of Cardiff developed a nifty technique for analyzing the hidden content in ancient parchment without having to open them, such as the original musical scores of Bach, or the Dead Sea Scrolls (some of which are so fragile and badly damaged, they haven't been unrolled yet).

Many manuscripts, such as those in the 12th century, used iron gall ink made from oak apples, but the parchment on which they were written contains collagen (since the parchment was made from the thinly stretched skins of cows, sheep, or goats), and collagen naturally degrades to gelatin. Iron ink speeds up the process. It's a wonder so many parchments survived, frankly.

Anyway, the Cardiff researchers used the synchrotron's powerful x-ray beams, to create 3D images of iron-inked documents. Because the inked lettering contains iron, the result is an absorption image, much like how one's bones show up so vividly on a standard x-ray. Rolled parchment works the best with the technique; books are flat and thick, which is a bit more challenging.

While x-rays can shed light on arty mysteries, sometimes it's not quite enough to crack the case. Maurizio Seracini -- a National Geographic Fellow and a cultural heritage engineer and founder of the Center of Interdisciplinary Science for Art, Architecture, and Archaeology (CISA3) at the University of California, San Diego -- is a self-described an "art diagnostician" who has been searching for a lost mural for 30 years. The artist? Leonardo da Vinci.

He's been working with other UCSD scientists to analyze 500-year-old bricks from a wall in Florence's Palazzo Vecchio. They are looking for a lost fresco called the "Battle of Anghiari" that Leonardo never completed and presumed to have been destroyed. Leonardo began the project to commemorate the 15th century Florentine victory over Milan at Anghiari in Tuscany, but he left the following year without completing the mural. To find it, the scientists are bringing all the high-tech ammo they can muster to the task: laser scanners, thermal imaging, radar, and neutron beams, among other techniques.

About 30 years ago, Seracini noticed a cryptic message on another fresco in the hall by another 16th century artist, Giorgio Vasari: "Cerca, trova," or "Seek, and you shall find." (The image is a scene from Paul Rubens' copy of the lost mural, painted around 1604.) This made him suspect that Vasari preserved Leonardo's unfinished fresco rather than destroying it. He also found bricks and stonework in a storeroom that were once part of the enormous hall, the Salone del Cinquecento ("Hall of the 1500s") in the Palazzo Vecchio. With the permission of Culture Minister Francesco Rutelli, he shipped off the bricks to UCSD so that scientists could analyze their structure and composition.

First, they used radar and x-ray scans to locate a cavity behind Vasari's fresco, indicating a space between walls, and then they used a laser scanner to construct a 3D model of Vasari's wall. Next they conducted a chemical analysis of Vasari's paint pigments, and thermal imaging to better delineate the wall structure. This gave them a better understanding of what might lie behind that wall in preparation for the final step: sending a flux of neutrons through the entire structure. Everything they learned about the pigments and walls could be subtracted from the overall neutron analysis, thereby establishing the composition of the wall Leonardo worked on.

If it's there, Seracini thinks the mural should be found right on top of the original stone wall of the hall. He could be wrong -- there might not be a lost Leonardo there at all. But Seracini's still looking. And he has yet another new technique at his disposal, capable of focusing trace amounts of gamma rays. Robert Smither, a physicist at Argonne National Laboratory’s Advanced Photon Source, is the inventor of the copper-crystal mosaic gamma ray diffraction lens, a tool that could very well be capable of photographing a painting through a wall of solid brick.

Photojournalist Dave Yoder, who got involved with the effort three years ago, tried a Kickstarter campaign to raise funds for the ongoing search; although National Geographic is providing generous funds for the project, the gamma ray lens is super-expensive, and needs additional outside resources. Yoder, for one, is convinced this could finally be the tool they need to crack the case:

Smither was optimistic that his technology, a particular kind of gamma camera that he is developing for medical use in high-definition tumor imaging, could work for this application. He and I travelled to Frascati, the location of the Italian research center ENEA, where in cooperation with a team of Italian physicists, we tested the technique. Using a particle accelerator straight out of a science fiction movie, the scientists recorded gamma ray signatures emitted from pigment samples that penetrated through the original bricks we had brought from the Palazzo Vecchio.

The results were very encouraging; Smither’s technology should work well to detect, and even image, the painting, even through Vasari's brick wall. Because we know from copies what the painting looked like, having an image could not only help positively identify the painting, should it survive, but could also offer information about its condition.

Alas, the Kickstarter campaign only raised around $25,000 of the necessary $266,500, despite media coverage in the New York Times, among other outlets. But it's certainly a start, and somehow I doubt a man like Seracini will give up now after searching for 30 years.

X-rays aren't the only physics tool helping to illuminate the secrets of art: a group of Italian and German scientists have used nuclear magnetic resonance -- the underlying physics behind MRI machines -- to non-invasively map out the layers of historical fine paintings . This is known as "stratigraphy." That includes any preparatory layers, under-drawings, the actual layers of paint, and in many cases, a layer of varnish.

The rationale for doing this at all is that this sort of precise analysis helps establish age, origin and authenticity of works of art, in much the same as geologists learn about the Earth's history by studying the various geological strata. The new technique does much the same thing for paintings as it does for the human body, except instead of using x-rays, detectors, and cutting-edge computers to provide information about soft tissue and the possible presence of tumors, it provides information about the binding agents used in the painted layers. Those agents were often made of things like egg yolk or oil.

Just knowing the nature of the binding agent can usually distinguish between a naturally-aged painting and one that has been artificially aged (a polite euphemism for "forged"). It's non-invasive, and the magnet used in single-sided, unlike MRI magnets which have to surround the patient (and/or limb) for imaging. So scientists can bring the scanner right up to the painting without ever touching the surface. Furthermore, the technique can determine the thickness of various paint layers, too, and while it can't definitively "date" each layer, it can tell which ones are older than others. It's easy to see why this might be a useful tool for art historians.

Isn't technology wonderful? Who knows what else science might find lurking beneath the surfaces of other paintings?