How did Leonardo paint The Last Supper ?
A mural that is not a real fresco: layers, oily tempera, slow execution, loss of material and twenty-two years of restoration.
Leonardo painted the wall like a panel
Instead of quickly applying pigments with water to a still damp coating, he prepared a dry, smoothed and bleached wall, then layered his colors with a greasy tempera. He could thus move slowly, correct, superimpose and shape the light.
The pigments remained on the surface instead of being incorporated into the coating by carbonating the lime. Humidity, building variations, dust and old interventions then accelerated uplifts and losses.
The Last Supper not a fresco in the technical sense
In common parlance, any painting on a wall is often called a "fresco". In art history, however, the word designates a specific process: painting on a still fresh coating.
The pigment enters the lime
- The painter prepares a portion of coating corresponding to a day of work.
- Water diluted colors are applied before drying.
- As it dries, lime fixes the pigments in a mineral matrix.
- The process requires speed, planning and few corrections.
The pigment remains on the surface
- Leonard smoothes and first prepares the wall, then waits until it is dry.
- It uses an organic binder, described by the museum as an egg-fat tempera.
- It works in layers, takes up details and modulates transitions.
- The colored layer adheres less closely to the support and can flake.
Four levels between masonry and image
The paint does not float directly on the brick. It depends on a succession of layers whose adhesion and stability determine its survival.
To paint slowly, change and nuance
A combination of internal fragility and material history
It would be too simple to blame a single material. The current state results from a system: technique not very compatible with a wall, difficult environment, building accidents and successive restorations.
Surface adhesion
Color is not mineralized in the coating. When the binder ages or the preparation deforms, the pictorial film may lose its cohesion and become detached.
Humidity and condensation
A cold and damp wall promotes support movements and salt transport. Even today, relative humidity is one of the closely monitored parameters.
Dust and pollution
The particles settle on an already porous and lacunar surface. The museum now filters the air and controls visitor entry.
Interventions and accidents
Cleaning, gluing, repainting and reconstruction changed the image. The bombing of 1943 destroyed much of the refectory around the wall.
Decline did not wait for modern centuries
1517: "it begins to deteriorate"
Antonio De Beatis observes the problem less than twenty years after completion. This testimony is crucial: it shows that the weakness of pictorial film does not only result from restorations or war.
1568: Vasari sees almost nothing but a stain
Giorgio Vasari's vocabulary is dramatic, but it confirms a rapid loss of readability. In 1625, Federico Borromeo still mentioned falling paint scales.
What historical photographs allow us to compare
An old photograph never shows the work "originally". It records a state already restored, darkened or repainted. Comparing the countryside above all reveals the way in which each era understood conservation.
A darkened and very repeated image
Anderson photography documents a surface whose readability depends largely on ancient interventions. Today it serves as a historical witness, not an original model.
After Luigi Cavenaghi
Cavenaghi seeks to consolidate painting and improve its reading. The photo reminds us that the notion of restoration is evolving: completing the image has not always been considered problematic.
The gutted refectory
The bombing collapses the roof, the vaults and a wall. The wall of The Last Supper, protected by makeshift devices, survives amid the ruins, but suffers a major environmental upheaval.
A museum built around a stable climate
The visitor enters through alternating doors that filter the air. Temperature, humidity and particles are monitored to slow down degradation mechanisms.
Restore without repainting the lost painting
Distinguish Leonardo from the layers added after him
The last major intervention does not seek to make the work "like new". It removes as much as possible the repaintings which masked the original fragments, consolidates fragile areas and restores a coherent reading without inventing what has disappeared.
The result, opened to the public in 1999, is deliberately less spectacular than certain previous images. The gaps are not transformed into false details: they are treated so that the gaze connects the preserved parts without confusing restoration and Leonardo's painting.
The best treatment is now preventive
Such a fragile work cannot be restored indefinitely. After 1999, the museum favored limiting the causes of degradation rather than repeated interventions on the surface.
Old copies complete the original without replacing it
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See reproductionTechnique and conservation of The Last Supper
Is the Last Supper a fresco?
No, not in the strict technical sense. Leonardo mainly painted dry on a white preparation, with a greasy tempera. A real fresco is painted on a damp coating which fixes the pigments as they dry.
Why didn't Leonardo use the traditional fresco?
Because it requires working quickly, in portions of fresh coating, with few possibilities for correction. Leonardo wanted to move forward slowly, take up the figures, superimpose the layers and obtain effects close to painting on panel.
When did the work begin to deteriorate?
Very early. Antonio De Beatis reported in 1517 that it was beginning to deteriorate, less than twenty years after its completion around 1498.
Did the 1943 bombing destroy The Last Supper?
No. He destroyed the roof, the vaults and part of the refectory, but the wall carrying the work survived thanks to protections. The painting environment was nevertheless profoundly disrupted.
How long did the last major restoration last?
The campaign led by Pinin Brambilla Barcilon began in 1977 and ended in 1999, more than twenty years.
Are all the colors visible today by Leonardo?
No. A significant part of the original material has disappeared. Modern restoration has removed many ancient repaintings, consolidated autograph fragments, and treated gaps in discernible and measured ways.
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