The brush and the scalpel: When art reveals itself under x-rays

Authenticating a work of art is a journey through time, an investigation where every detail matters—the chemical composition of a pigment, the wear of a frame, the trace of a forgotten brushstroke beneath layers of paint. It is also a silent battle against forgers, those illusionists who, for centuries, have played with our desire to possess beauty. How do we distinguish the real from the fake when a single brushstroke can transform a canvas from obscurity to fortune? When a painting leaps from €10,000 to €100 million on the strength of a signature alone? Art expertise is not an exact science, but an art in itself, where intuition, erudition, and cutting-edge technology intertwine.

01The ghosts beneath the paint: when science reveals the invisible

Imagine for a moment that you could see through layers of paint, as if time had suddenly frozen. This is precisely what modern analytical techniques allow, turning every painting into a stratified archive of its own past. Infrared reflectography, for example, acts like a time machine. When it scans Picasso’s Les Demoiselles d’Avignon, it reveals a very different initial composition beneath the Cubist forms: a sailor and a medical student were originally planned for the scene before the artist erased them, leaving only the five enigmatic figures we know today. These pentimenti—an artist’s changes of heart—are like involuntary confessions, tangible proof of the hand that held the brush.

X-radiography, meanwhile, functions like a medical X-ray, revealing the internal structure of a work. When it passes through Rembrandt’s The Night Watch, it uncovers an additional figure: a young boy whose ghostly silhouette was later covered by a layer of paint. These discoveries are not mere curiosities; they are irrefutable evidence of authenticity. A forger, no matter how talented, cannot reproduce these hidden revisions. They often ignore that the great masters worked in successive layers, modifying their compositions as their vision evolved.

Ultraviolet light reveals another dimension of a work: its state of preservation. Under its harsh glow, restorations appear as dark patches, betraying successive interventions. An old painting should display a characteristic network of cracks, called craquelure, which forms naturally over time. These fissures, like wrinkles on skin, tell the story of the support—the fluctuations in humidity, temperature changes, the journeys across centuries. A modern forgery, even artificially aged, will never exhibit this organic, unique network.

02The signature: a clue, never proof

The signature is often the first element examined, as if this simple scrawl could solve everything. Yet it is as deceptive as a distorting mirror. Take, for example, Woman with a Fan, attributed to Modigliani. For decades, this canvas was considered authentic, its signature in the bottom right corner seemingly unassailable. Until an X-ray analysis revealed that this signature had been added after the painting was completed, like a fake tattoo on skin already marked by time. This case is far from isolated: the fake Renoirs of the 1920s, the fake Corots of the 19th century—all bore convincing signatures that fooled even the greatest experts.

Artists themselves played with their signatures, as if with a secret code. Dürer signed his works with an enigmatic monogram, an intertwined "AD" resembling a medieval seal. Caravaggio, even more discreet, sometimes hid his name in the reflections of armor or carafes. Conversely, masters like Leonardo da Vinci almost never signed their works, believing their style alone was enough to identify them. The Mona Lisa, The Last Supper, The Virgin of the Rocks—none bear his signature, yet their authenticity is unquestioned.

Renaissance workshops further complicate matters. When a collector buys a canvas attributed to Rubens, they are in fact acquiring a work executed by several hands—that of the master for the most important parts, those of his assistants for the backgrounds and details. Where does the original begin, and where does the copy end? This question has haunted experts for centuries. The Catalogue Raisonné of Rembrandt, published in 1989, halved the number of works attributed to the master, sending shockwaves through the art world. Paintings displayed in the greatest museums suddenly lost their pedigree, demoted from masterpieces to workshop productions.

03The secret language of pigments

If paintings could speak, they would tell stories of travel, trade, and technological revolutions. Their pigments, in particular, are like chemical fingerprints, revealing the era and sometimes even the place of their creation. Ultramarine blue, made from lapis lazuli imported from Afghanistan, was more precious than gold in the Middle Ages. Its presence in a 14th-century canvas is thus a valuable clue—unless a forger used a modern, far less costly pigment. X-ray fluorescence spectrometry can distinguish these ancient blues from modern imitations, revealing their atomic composition with diabolical precision.

Emerald green, which appeared in the 19th century, is another temporal marker. This toxic pigment, based on arsenic, was highly prized by the Impressionists. Its presence in a painting purportedly from the 17th century would be a glaring anachronism. Similarly, titanium white, invented in 1916, never appears in works created before that date. These chemical details are like molecular clocks, allowing a work to be dated with remarkable accuracy.

The binders used to mix pigments tell another part of the story. Renaissance painters used linseed or walnut oil, while 20th-century artists adopted acrylics. Chromatographic analysis can distinguish these binders, sometimes revealing flagrant inconsistencies. A fake Vermeer, for example, might feature modern pigments mixed with linseed oil—a combination that would never have existed in the Dutch master’s time.

04Provenance: a detective story across the centuries

A work’s provenance is like its family tree—a succession of owners, sales, and exhibitions that guarantee its authenticity. A canvas without provenance is like a diamond without a certificate: its value remains uncertain, its history suspect. Take the case of Salvator Mundi, attributed to Leonardo da Vinci. Its journey is a novel in itself: part of Charles I of England’s collection in the 17th century, lost for decades, resurfacing at a Louisiana auction in 2005 for $1,175, then sold for $450 million in 2017 after a controversial attribution. Every step of this story has been meticulously documented, from royal inventories to sales catalogs, including old photographs.

Yet provenance can also be a trap. The most skilled forgers fabricate convincing histories from scratch, complete with fake documents and invented provenances. The Beltracchi affair is a case in point. This German forger managed to sell fake Max Ernsts, Heinrich Campendonks, and Fernand Légers by creating a fictitious provenance: the "Jäger" collection, supposedly hidden during World War II. To make his story credible, he even artificially aged the labels on the backs of the canvases and forged exhibition catalogs.

Archives are therefore essential. Catalogues raisonnés—reference works that list all authenticated works by an artist—are indispensable tools. Daniel Wildenstein’s Catalogue Raisonné of Monet, for example, records over 2,000 of the master’s canvases. But these catalogs are not infallible. They evolve with new discoveries, reattributions, and technologies. A work excluded from a catalogue raisonné may be reinstated years later, as was the case with Modigliani’s Seated Woman, long considered a fake before being rehabilitated in 2018.

05Forgers: the dark magicians of art

They are the black magicians of the art world, capable of transforming an anonymous canvas into a masterpiece with a few brushstrokes. Their story is as fascinating as that of the artists they imitate. Han van Meegeren, perhaps the most famous of them all, went so far as to sell a fake Vermeer to Hermann Göring during World War II. When arrested for collaboration, he had to prove his innocence by painting a new fake Vermeer under police surveillance. The result, The Supper at Emmaus, was so convincing that it fooled even the experts of the time.

Elmyr de Hory had a different approach. This Hungarian forger, who inspired Orson Welles’ F for Fake, specialized in drawings by Modigliani, Matisse, and Picasso. He didn’t copy existing works but created drawings from scratch in the masters’ styles, with such mastery that he deceived the greatest dealers. His technique was simple: he used old paper, artificially aged inks, and, above all, he knew the weaknesses of experts. "An expert who says ‘it’s a fake’ is afraid of being wrong," he said. "The one who says ‘it’s an original’ is confident. That’s the one I target."

Modern forgers have added a new weapon to their arsenal: technology. Today, software can artificially age canvases, reproduce realistic cracks, even clone signatures. Some use 3D printers to replicate the texture of impasto. Yet despite these advances, the best forgers remain those who master the old-fashioned art. Wolfgang Beltracchi, arrested in 2010, painted his fakes himself, using pigments and techniques identical to those of the masters he imitated. His secret? An encyclopedic knowledge of materials and infinite patience. To age his canvases, he exposed them to the sun, rolled and unrolled them hundreds of times, until he achieved a perfect network of cracks.

06The eye and intuition: when expertise becomes an art

Despite technological progress, the human eye remains irreplaceable. Giovanni Morelli, a 19th-century Italian physician, revolutionized art expertise by developing a method based on observing details. According to him, great masters had "brush tics," particular ways of painting ears, hands, or folds of clothing. These details, often overlooked by forgers, are like invisible signatures. Morelli was thus able to reattribute many works by studying these anatomical peculiarities.

This intuitive approach is still used today. When an expert examines a canvas attributed to Van Gogh, they look for subtle clues: the way brushstrokes follow contours, the texture of impasto, the rendering of light. A fake Van Gogh may imitate the colors and subjects, but rarely that characteristic energy, that vibrant touch that seems almost alive. Similarly, a fake Modigliani might have the elongated forms and almond-shaped eyes, but rarely that stripped-down elegance, that economy of means that defines the Italian master.

Yet even the best experts can be wrong. Bernard Berenson, the "pope" of Italian Renaissance art, mistakenly attributed many works to masters like Botticelli or Raphael. His errors, revealed after his death, cast a shadow over his reputation. Today, experts work in teams, cross-referencing their observations to minimize the risk of error. But intuition remains key. As art historian Ernst Gombrich once said, "The eye sees only what the mind is prepared to understand."

07The future of authentication: between AI and blockchain

The world of art expertise is undergoing a transformation. Artificial intelligence is making its way into laboratories, with algorithms capable of analyzing thousands of paintings in seconds. Startups like Art Recognition are developing software that compares works to image databases, detecting stylistic inconsistencies with formidable precision. Yet these tools have their limits. AI can spot similarities, but it struggles to grasp historical context, the artist’s intentions, or the subtleties of a brushstroke.

Blockchain, meanwhile, promises to revolutionize the traceability of artworks. Platforms like Verisart allow authentication certificates to be recorded on a blockchain, making forgery impossible. Yet this technology does not solve the problem of physical authenticity. A work can have a tamper-proof certificate while still being a perfect fake. Blockchain guarantees provenance, not artistic quality.

The future of expertise may lie in a hybrid approach, combining technology and human know-how. Collaborative databases, like The Rembrandt Database, already allow experts worldwide to share their knowledge. Museums are opening their archives, making thousands of documents previously reserved for specialists accessible to all. This democratization of expertise could be the key to combating forgers.

08The last word: when art resists analysis

At its core, authenticating a painting is an endless quest, a dialogue between the visible and the invisible, the tangible and the intangible. The most sophisticated techniques will never fully capture what makes a work magical: that spark of genius, that emotion that transcends centuries. A Van Gogh painting is not just a canvas covered in pigments; it is a window into the artist’s soul, a fragment of their time captured for eternity.

Forgers know this well, those who spend their lives trying to replicate this magic without ever quite succeeding. Their copies may deceive experts, machines, collectors, but they never deceive time. For time does not lie. It leaves its marks on authentic canvases—those cracks that tell centuries of history, those pigments that have traveled across continents, those pentimenti that reveal the hesitations of great masters.

So the next time you stand before a painting, remember: what you see is only part of the story. Behind every brushstroke lie secrets, lies, buried truths. The art of expertise is precisely this: knowing how to read between the lines, to hear the whispers of the past, and to discern, in the silence of museums, the voices of true geniuses.