Intervention
Because of the seriousness of plaster detachments it was necessary, as first intervention, applying a protective gauze to attach the fragments, at the moment without the arriccio layer and about to fall, to the wall support. This operation was necessary to be able to consolidate the plaster later on, limiting the risk of collapses. Cleaning of incoherent deposits was carried out with soft brushes, in order to allow adequate adhesion of the cotton facing, applied with a high-concentration acrylic resin.
Consolidation aimed to re-establish the arriccio layer, at that point missing or completely crumbling, using a lime-based mix compatible both with the limestone of the wall and with the materials of the plaster. The reverse side of plaster was mechanically cleaned, by inserting flexing wooden probes through existing lacunae or through perforations in the cement edges realized just after discovery. After having washed the wall support with water and alcohol, it was possible to inject the consolidation mix, composed of brick dust, hydraulic lime and lime putty.
To avoid making the fragments dangerously heavy, since some of them were supported only by the facing, consolidation was realized gradually. Void areas were filled layer by layer from the bottom towards the top, giving 24 hours intervels, so to allow water evaporation and drying of mortar, keeping a constant control over the intervention. Small plaster detachments on the arches were consolidated with injections of acrylic resin in a water emulsion. The same consolidant, in lower concentration, was used to infiltrate areas of detached plaster.
After removing the facing of the fragments, an appropriate methodology for cleaning the painting film was devised, by testing different solvents. The surface was at the moment totally illegible in the Eros and Psyche representation and extremely glossy on the arches. It was altered by deposits of coherent dust and by a thick layer of resin, probably vinyl, applied in the past. Organic solvents were used to remove the glossy film, and weakly alkaline solvents to clean coherent deposits.
Some old stuccoing, at that point altered, was removed mechanically, and plaster lacunae were filled with mortar composed by lime putty and local limestone powder. Then, areas of missing color were integrated with watercolor shades. This operation aimed to improve the legibility of representations and their stylistic and chromatic qualities, by lowering the intrusive tone of lacunae, without pretending to perform a hasty and unreliable reconstruction of missing parts.
Wide areas with no plaster, as for example the arches, were treated by simply applying mortar composed of lime putty and limestone powder, chromatically similar to the general tones of the site, in order to re-establish the uniformity of decoration and to preserve an idea of a wall cover now not existing anymore.On the areas of wall left exposed by the total loss of painted plaster, joins between ashlars were pointed with a material similar to the original one, composed of clay mud, river sand, chopped straw and pellets.
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