by Mauro Civai

The interventions of restoration regarding the facade of the Palazzo Pubblico of Siena were directed by the architect Stefano Amidei. Considering the vast quantity of material to be restored, the dire state of degradation and the enormous artistic and historical value of the monument, it was necessary that the very first phase of the operation consisted of an extensive set of studies and investigations, aimed at identifying the causes of the degradation. These studies were carried out mainly by the Department of Archaeology and Environmental Geo-chemistry of the University of Siena.

On the basis of the results of these analyses, precise interventions were designed and prepared for the necessary conservational restoration: this would involve a skilled team of specialized restorers capable of working simultaneously on stone materials, plasterwork, and metals. The first interventions were carried out in order to eliminate the effects of atmospheric deposits, black crusts, sulphurization, organic and bio detergent deposits, and to reduce, where possible, the causes of these above phenomena.

For the cleaning of the surfaces and the elimination of the effects of degradation, mechanical, chemical, and physical-mechanical methods were utilized, as in the case of LASER technology, the use of which allowed the restorers to resolve a condition that affects some sites where it is not always possible to use water for the chemical cleaning and where consolidating substances cannot be used due to the level of decrepitude of the underlying surface. In these cases, the laser allows the execution of a self-limiting cleaning that is selective and discriminating, conserving the glazes and colours present beneath the unwanted black crusts.

Other interventions were those connected to the glazes and protection.

Numerous activities were carried out on the building through dismantling and reconstructions: research allowed the recuperation of the chromatic balance between parts of the surface of the wall structure.

For the decorative parts of the building, comparisons were made in order to establish the original chromatic selection. Traces of the original colours were found during the stratographic investigations and the cleaning, the first task was to register and conserve what remained, even if this was only just a trace.

During the following phase, and in agreement with the Superintendence, it was decided not to propose a chromatic reconstruction that was no longer coherent to the current state of the facade, but to base the selections upon different plan volumetric relationships. This decision was in keeping with previous choices that had been made relating to the aesthetics of the facade.

During this phase it was also decided to use a scaffold to collect photographic images in order to register as much information as possible in as much detail as possible.

A mapping of all the various types of materials was then carried out, the state of their degradation divided into differing themes, the techniques involved in their construction, and all the remaining traces of previous interventions and modifications.

During the restoration itself, continuous documentation registered the details of each intervention.