The black that devours light: When judean bitumen consumes 19th-century masterpieces

This phenomenon, which conservators today call with a hint of dread "bitumen disease," is no isolated case. In the storerooms of Europe’s great museums, hundreds of 19th-century canvases bear the scars of this cursed pigment. Géricault’s The Raft of the Medusa is covered in a network of dark cracks that eerily evoke the rotting planks of the shipwreck. Turner’s tempestuous skies, once streaked with golden lightning, have turned to opaque fog. Even Courbet’s realist landscapes gradually lose their earthy nuances, as if the very ground were crumbling before our eyes. These works, meant to immortalize the passion of an era, are self-destructing before us—and the culprit bears a poetic name: Judean bitumen.

01The painters’ black gold: a fatal passion

To understand this pictorial tragedy, we must trace the origins of this fascination. Judean bitumen, that viscous, black substance extracted from Middle Eastern deposits, was no recent discovery in the 19th century. The Egyptians had already used it for embalming, the Babylonians to waterproof their constructions. But it was with the rise of oil painting and the craze for chiaroscuro effects that European artists adopted it systematically.

What so enchanted painters was its ability to create shadows of unparalleled depth. Unlike traditional blacks like ivory or charcoal, bitumen offered a velvety transparency that allowed for remarkably subtle glazes. Mixed with linseed oil, it spread in thin, luminous layers, capable of suggesting both the gloom of a forest and the darkness of a moonless night. Delacroix mastered its use in Liberty Leading the People, where he employed it to model the folds of the flag and the faces of the insurgents. Turner, for his part, nearly abused it, incorporating it into his skies to create effects of almost supernatural transparency.

But what made bitumen so powerful was also its weakness. Unlike mineral pigments such as lapis lazuli or cinnabar, bitumen is an organic substance, a hydrocarbon that never truly dries. It remains perpetually in a semi-liquid state, like a wound that never heals. Over time, it oxidizes, darkens, and eventually shrinks into a network of cracks that irresistibly evokes the dried skin of a fruit left in the sun.

02The chemists’ laboratory and the madmen’s studio

The history of bitumen in 19th-century painting is also that of an era when art and science maintained tumultuous relations. Artists, hungry for new techniques, turned to recent chemical discoveries to renew their palettes. Bitumen was one of these miracle products, alongside Prussian blue and chrome yellow, promising to revolutionize painting.

In Parisian studios, experimentation never ceased. Some painters, like Paul Delaroche, mixed bitumen with wax to achieve matte, velvety effects. Others, like Théodore Chassériau, used it in glazes to soften transitions between shadows and light. Turner, ever in search of new textures, even incorporated bitumen into his canvas preparations, creating a dark ground that, in his words, was meant to "make the colors sing."

But these experiments came at a price. The chemists of the time, like Jean-François Léonor Mérimée (the writer’s father), warned of the dangers of unstable pigments. In his On Oil Painting, published in 1830, he already described the risks of bitumen, noting that "this substance, so useful for shadows, has the flaw of never drying completely and darkening over time." Yet these warnings were largely ignored. Artists, swept up in their enthusiasm, preferred to trust the promises of color merchants over the cautions of scientists.

Géricault’s case is particularly revealing. For The Raft of the Medusa, he used an impressive quantity of bitumen, especially in the shadows of the sky and sea. Contemporaries were struck by the dramatic intensity of these dark areas, which seemed to absorb light like a black hole. But by the 1830s, observers began to notice that the painting was "aging poorly." Cracks first appeared in the thickest areas, then spread like a spider’s web. Today, Géricault’s masterpiece bears the scars of this reckless experimentation, and the Louvre’s conservators must monitor its evolution constantly.

03The curse of shadows: when painting turns against itself

What makes the case of bitumen particularly poignant is that it is not merely a matter of material degradation, but a true betrayal of artistic intent. 19th-century painters used it precisely for its expressive qualities—its ability to create deep shadows, mysterious atmospheres, and chiaroscuro effects reminiscent of 17th-century masters. But over time, these shadows have transformed into veritable black holes, swallowing details and unbalancing compositions.

Take Delacroix’s The Death of Sardanapalus. In its original version, the painting’s shadows were designed to highlight the nude bodies of the women and the shimmer of precious fabrics. Bitumen, applied in glazes, created a depth that drew the eye toward the center of the composition. Today, those same shadows have darkened so much that they form a compact, opaque mass, like a wall blocking the view beyond. The faces of the figures, once expressive, are now half-erased. The painting, meant to depict the chaos of destruction, seems itself to be disintegrating.

This phenomenon is even more striking in Turner. His skies, once streaked with golden light and diaphanous clouds, are now covered in a brownish layer that smothers all transparency. In The Slave Ship, the tumultuous waves and stormy sky, meant to convey movement and drama, now appear as an amorphous, dark mass. Bitumen, intended to suggest spatial depth, has ended up flattening everything.

This inversion of artistic intent is particularly ironic in the case of Romantic painters. These artists, who celebrated the power of nature and the fragility of human existence, saw their works literally consumed by time—a central theme of their own aesthetic. Bitumen, meant to represent fleeting beauty, has become the very symbol of that transience.

04Conservators face the monster: can we save the sick paintings?

Confronted with this epidemic of darkening, museum conservators find themselves in a cruel dilemma. Should they let the paintings evolve, risking their complete disappearance? Or attempt restorations, with the danger of distorting the original work?

Modern techniques offer solutions, but none are perfect. One of the most promising approaches is the use of lasers to selectively remove layers of oxidized bitumen. In 2018, the Louvre treated The Death of Sardanapalus with an ultra-short pulse laser, capable of targeting darkened areas without damaging the underlying paint layers. The results were spectacular: details that had vanished for decades reappeared, as if by magic.

But this technique has its limits. It cannot be applied to all works, particularly those where the bitumen layer is too thick or too mixed with other pigments. Moreover, it does not halt the degradation process—it merely slows it. Paintings treated this way must be monitored constantly and often placed in strictly controlled conservation conditions (regulated temperature and humidity, dim lighting).

Another approach involves using special varnishes to isolate the bitumen from the rest of the paint. But here, too, the remedy can be worse than the disease. Some varnishes yellow with age, altering the original colors. Others may react chemically with the bitumen, accelerating its degradation rather than slowing it.

The most radical—and controversial—solution would be to completely remove the bitumen from the paintings. But this operation is extremely risky. As bitumen ages, it blends intimately with other paint layers. Removing it would often mean removing part of the original composition. Furthermore, the substance was sometimes used in preparatory layers, making its elimination nearly impossible without damaging the canvas itself.

Faced with these difficulties, some conservators advocate a more minimalist approach. Rather than attempting aggressive restorations, they propose meticulously documenting the evolution of the paintings, using advanced imaging techniques like radiography or infrared reflectography. These methods reveal the underlying layers of paint, offering a glimpse of what the work originally looked like.

05Bitumen and the soul of the 19th century: an unintended metaphor

Beyond its material consequences, the degradation of bitumen in 19th-century painting offers a fascinating metaphor for the spirit of the age. The artists who used it with such enthusiasm were the same ones who celebrated revolution, individualism, and the power of emotion. They sought to break academic rules, explore new techniques, and capture the very essence of modernity.

In this context, bitumen appears as the perfect symbol of their approach. It was a new, bold material that allowed for unprecedented effects. But it was also an unstable, unpredictable substance that defied the traditional laws of painting. By using it, artists took a risk—just as they took risks in tackling controversial subjects or experimenting with revolutionary styles.

This risk-taking is particularly evident in Romantic painters. For them, bitumen was not just a pigment—it was a means of expressing the darkness of the human soul, the destructive power of nature, the fragility of existence. In The Raft of the Medusa, Géricault used it to create an atmosphere of absolute despair. In The Death of Sardanapalus, Delacroix made it the instrument of an orgy of destruction. Even Courbet, who employed it more discreetly, used bitumen to ground his landscapes in a tangible, earthy reality.

There is something deeply poetic in the fact that these works, designed to capture the ephemeral, are themselves victims of ephemerality. The paintings meant to immortalize the passion of an era are self-destructing, as if time itself refused to let them fix the moment. This tragic irony would not have displeased the Romantics, who saw in beauty the very mark of its own disappearance.

06The legacy of bitumen: what modern artists have learned

The story of bitumen in 19th-century painting is also a lesson for contemporary artists. It reminds us that technical innovations, however seductive, must be used with caution. Today, painters have access to a palette of synthetic pigments of remarkable stability, but the risk of degradation has not disappeared entirely.

One of the most important lessons from this saga is the importance of documentation. Modern artists are encouraged to meticulously record the materials they use and the techniques they employ. This practice, which could have saved many 19th-century works, has now become a standard in the art world.

Another legacy of bitumen is the development of preventive conservation science. Modern museums pay particular attention to the storage and exhibition conditions of works. Temperature, humidity, lighting—everything is controlled to minimize degradation risks. Sensitive paintings, like those containing bitumen, are often placed in specially designed display cases to protect them.

Finally, the history of bitumen has changed how we appreciate art. Today, we understand that works are not immutable objects but living entities that evolve over time. This awareness has led to a more nuanced approach to restoration. Rather than trying to "repair" paintings to return them to a supposed original state, conservators now aim to preserve their authenticity, including the marks of time.

07Epilogue: when painting looks back at us

There is something deeply unsettling about the sight of 19th-century paintings consumed by bitumen. These works, meant to speak to us of beauty, passion, and rebellion, now seem to question us in return. What remains of our own creations? What will become of our artistic legacy in a hundred years, in two hundred?

Gazing at The Death of Sardanapalus in its Louvre display case, one cannot help but think of the fragility of all human endeavor. Delacroix sought to capture the very essence of destruction—and now his painting, in turn, is being destroyed before our eyes. This tragic irony reminds us that art, like life, is a precarious balance between creation and disappearance.

Perhaps this is the ultimate lesson of Judean bitumen. In its spreading darkness, in its spreading cracks, it speaks to us of fleeting beauty, the power of time, and the necessity of creating despite everything. For it is precisely this fragility that makes the masterpieces of the 19th century so moving. They are not perfect, immutable objects but living witnesses of a bygone era—and of our own humanity.