Stolen art is tough to get rid of. A collector doesn’t want to invest in a painting that will be turned over to the authorities. In the mid-nineties, outside Philadelphia, three crooks broke into the country home of William Penn and snagged around fifty artifacts; when the theft made the papers, they threw the art in plastic bags and dumped them into the Delaware River. Three years ago, five paintings were stolen from the Musée d’Art Moderne, in Paris, and the burglar decided to stash them in a dumpster. Just his luck: the bin was picked up by a trash compactor, which munched thoughtlessly on Picasso, Matisse, and Modigliani, with Braque and Léger for dessert.

Last October, seven works of art were swiped from the Kunsthal museum, in Rotterdam: Picasso and Matisse, again, plus two Monets, a Gauguin, a Meyer de Haan, and a Lucian Freud. The entry set off an alarm, but when police arrived at the scene, the culprit had already vanished. This past January, investigators arrested a Romanian man named Radu Dogaru on charges of carrying out the heist.

His mother, Olga Dogaru, was understandably upset. She began to think of things that other mothers of art thieves have considered in the name of protecting their sons. In 2001, Mireille Breitwieser, the mother of the notorious French art thief Stéphane Breitwieser, dispensed with her son’s stolen goods by tossing them in the Rhine-Rh?ne canal, chopping them up into pieces, and incinerating a few items. In February, Olga Dogaru told the police that she had put the evidence of her son’s crime in the stove, and set it aflame.

One month later, forensic specialists collected the ashes from her house. Romanian scientists began sifting through charred refuse from Olga Dogaru’s stove using optical and electronic microscopy—a “screening process, essentially,” to recover tiny particles of debris, said Tom Tague, a chemist at Bruker Optics and a member of the advisory board of the Metropolitan Museum of Art. “There has been such an awakening in the art community to use this kind of analysis,” which has existed since 1990 or so, he explained.

Upon arrival at a crime scene, if investigators were to find nothing more than black ash, analyzing any of it would be impossible. “But fortunately, that’s never really the case,” Tague said. “If things are charred, then you can typically identify which artist would have generated the art.”

It’s a delicate process. The eye can only see something as small as seventy-five microns, or about the width of a strand of hair. “You’re looking for particles much smaller than that,” Tague said. “So it’s tedious, really tedious. And you don’t want to disturb a crime scene. So it could take weeks or months just to recover the particles.” Even just two or three microns of dust could be the key to identifying the signature of Picasso.

“From a forensic standpoint, for evidence, you’re going to be looking for specific components of a painting,” said Robert Wittman, who joined the F.B.I. in 1988 and helped start the bureau’s Art Crime Team. Wittman says he has recovered three hundred million dollars worth of art in his career, which he describes in a book, “Priceless: How I Went Undercover to Rescue the World’s Stolen Treasures.” He told me, “In an oven, you’re going to be looking for things like metal, fasteners, nails, trace elements of the paints. There were some early paints that had lead in them. There was toxic yellow paint that French Impressionists used that had arsenic in it, and arsenic is a compound that doesn’t break down in a fire.” Dr. Ernest Oberlander-Tarnoveanu, the director of Romania’s National History Museum, said that analysts found “small fragments of painting primer, the remains of canvas, the remains of paint,” as well as copper and steel nails, according to the Associated Press. He told me by e-mail that they also found “fragments of painting with imprints of the oil painting reproduction.” Gheorghe Niculescu, the head of the team from Romania’s National Research Investigation Center in Physics and Chemistry, told Reuters that they uncovered “Prussian Blue, a paint pigment discovered around 1715 and used on a large scale by painters from around 1750.”

After sorting out the relevant particles, the Romanian team used X-ray-fluorescence and X-ray-diffraction techniques to identify which elements the fragments contained. This isn’t ideal for organic materials, but it’s a common first step for forensic analysis, Tague said, and “it could work reasonably well because many of the pigments are inorganic-based.”

“You can visually see what is there,” he went on, “but you don’t know what it is without doing spectroscopy.” Infrared and Raman microspectroscopy, which study the way molecules interact with light, are used for the purpose of authentication. By collecting both the infrared and Raman spectrums of a painting, an analyst can compare the molecules of the evidence to original works from the same period. “No two molecules interact with light the same way, so it’s really specific,” Tague said. “These are common tools in every art institute and forensics lab.”

On Monday, Olga Dogaru appeared before the court in Romania, alongside her son, and told a panel of three judges that, actually, she did not burn the art. According to the New York Times, she testified that it had all been a lie: “I believed that what I said before was the best thing at the moment, that this was the right thing to do.”

Meanwhile, Niculescu, of the Romanian investigative team, assured Reuters that they had “gathered overwhelming evidence that three (of the seven) paintings were destroyed by fire.” But he could not say which of the stolen paintings they had identified, or how he could be certain that these were the works lifted from the Kunsthal museum, which declined to comment on the police investigation. The forensic scientists are continuing to complete their report, and the Dogarus’ trial is set for next month. “Our task was to establish if the ash samples provided by the public prosecutor [contained] traces of substances and implements used to make paintings—for example, nails used to fix the canvas on chassis, substances used to prepare the painting primes, and pigments used by professional painters to prepare the oil colors,” Oberlander-Tarnoveanu told me. “So far, we were not asked to do authentications.” The museum confirmed to me that “the expertise just aims to establish if remains which may originate from nineteenth-to-twentieth-century paintings were identified in the investigated material.”

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