Many paintings were hard hit by the war in Italy, but few suffered the same level of damage as the Last Supper.
On 16 August 1943, most of the Santa Maria delle Grazie complex was reduced to rubble by Allied bombing raids. The refectory vault and walls also collapsed, yet the wall bearing the Last Supper remained standing although not entirely unscathed. Leonardo’s painting was exposed to the elements and received only inadequate attempts at protection. When examination was finally possible three years later, the painting’s condition seemed desperate: “... the surface was swollen by moisture and looked like rubbery cloth. The colour and even the underlying priming came away at the slightest touch...”, in the words of Soprintendente Wittgens.
It has always been known that in painting The Last Supper Leonardo used an experimental technique presumed to be a secco, but it does not appear to correspond to any a secco technique documented in the contemporary manuals. Nobody knows what type of medium he used, although it seems reasonable to suppose he used a mixture of binding media. The materials he used to build up the layers underlying the paint film are also a mystery.
One plausible suggestion is that this work is similar to a panel painting and as such very susceptible to attack by moisture. Since Antonio de Beatis’s first reference to the problem just twenty years after the work was completed, moisture has always posed the greatest threat to the Last Supper. This is now correctly attributed to condensation, and has been since the eighteenth century. Unfortunately restoration work on the Last Supper became intensive in the mid-nineteenth century and, worse still, the composition of the series of wonder products used was invariably a trade secret that could not be disclosed. In all probability they must have consisted mainly of animal gums and resins which are notoriously sensitive to heat and moisture.
In 1924 Oreste Silvestri used heated metal rollers in a misguided attempt to iron the raised paint film back into place, which explains why the wall painting is crushed and full of roughness and irregularity and why it appears unpleasantly dull with a greasy, glistening appearance when lit from the side.
This also explains why the work is so fragile and radically damaged both in appearance and in the material structure of its constituent layers. Because the surface has been treated with so many so-called fixatives, it is now less permeable than before but also much more prone to attract dust and pollutants. The underlying layers have become less and less cohesive due to innumerable microfractures and are now more pervious and unstable. It became pointless to continue consolidating the work and a few years after his restoration work, Silvestri was forced to admit that matters had by no means been resolved. A new attempt could have been made to consolidate the work after the war, but morale was low throughout Italy and the painting was by now in a sorry state.
An attempt was nevertheless made to improve the environment by preventing condensation. To this end, a radiant panel heating system was installed beneath the refectory floor. This was only a partial measure because it did not take into consideration other causes contributing to the damage.
Ironically enough, the painter and restorer Luigi Cavenaghi had pinpointed the problem and suggested solutions half a century earlier: “It is absolutely necessary to provide the Last Supper with a stable environment and protect it against the considerable amount of dust that is bound to be generated in such a frequently visited place. The door between the refectory and the cloister should therefore be sealed or made into a double door because it admits draughts which could affect the painting directly or change local atmospheric conditions. The catches of windows near to the painted wall should also be kept fastened for the same reason”. With the advent of environmental pollution this century it became necessary to view the whole problem of the Last Supper in a new light by examining the relationship between the work of art and its environment.
Scientific tests were therefore undertaken in order to establish conditions inside and outside the refectory, within the building as a whole, and on the Last Supper wall. Just under one hundred investigations were carried out. Some were scientific, but others were historical and involved research institutes and specialists throughout Italy and abroad. The Istituto Centrale del Restauro in Rome then had to sift through an immense pile of often disparate results in order to arrive at some sort of cohesive overall approach.
Their guiding principle was to interfere as little as possible with the interactive relationship between the work of art, its support structure (wall) and the environment. This ruled out direct, invasive conservation. Because the most severe problems to be tackled were the presence of dust and pollutants, changes in temperature and moisture levels and the suitability of the lighting (both artificial and natural), the following strategy was adopted: visitors may only visit the work in one direction (entering through the door in Piazza Santa Maria dell Grazie and leaving through the garden alongside). A restricted number of visitors will have to walk through specially insulated, air conditioned rooms designed to remove dust and pollutants before entering the refectory itself. By the time visitors reach the area surrounding the Last Supper, they will therefore be cleansed of dust and pollutants as far as possible. Their heat and moisture levels will also have balanced as far as possible without actually asking them to strip off and hold their breath. Not more than twenty-five people will be allowed to view the painting at one time, and an air filtration system will be installed.
An experimental lighting system reconciles the needs of illumination with conservation. This complements natural light sources, which have been controlled by applying automatic micro-blinds to the windows. It was decided not to take the easier option of screening the windows because this would have prevented the Last Supper from being viewed within the architectural context for which Leonardo originally painted the work.
Light filters have been introduced on the cloister wing adjacent to the refectory despite the potential problem of excessive heat and light this could introduce. Screening the windows would have imposed an artificial visual barrier between the refectory and the rest of the Santa Maria delle Grazie complex. Monitoring units and sensors have been fitted to ensure the local micro-climate and air quality are kept under control. The Last Supper wall has already been subject to monitoring for several years.
Restoration will resume when the refectory is re-opened to the public this month following completion of the building work. The organisations responsible for the operation (Soprintendenza ai Beni Ambientali ed Architettonici and Soprintendenza ai Beni Artistici e Storici, co-ordinated by the Istituto Centrale del Restauro) wish to keep the painting open to the public even during the restoration. So far this has been achieved, although the refectory recently had to be closed to comply with safety regulations. The Last Supper will undergo continuous monitoring once restoration is complete.
It will be an enormous task to fill all the gaps in this sadly mutilated and depleted work, to say nothing of cleaning the painting. In theory, all foreign deposits and material introduced during previous restorations should be removed, although in practice it will only be possible to do what is feasible to restore the work and return it to its original form.