INTRODUCTION
The mural paintings which decorate the internal part of the apse of the Parish Church of San Lorenzo in Borgo San Lorenzo were carried out by Galileo Chini in 1906, probably in one of his first artistic experiments in Mugello. The painting, carried out from the example of the antique Roman mosaics, portrays the Benedictory Christ in mandorla between the Saints Lorenzo and Martino, and blends the elegant modernist inflections with the medievalism of the general harmony.
The technique of the realization is that which is typical of Galileo Chini: a ‘dry’ painting, carried out by spreading the pigments over the dry plaster with the aid of a binder of an organic nature, which unfortunately it has not been possible to precisely identify, even with the help of chemical analyses, because of the advanced state of deterioration of the pictorial film. Because of the technique used, the daily junctures are not noticeable; the pictorial plaster, very thin, was spread directly over the wall parameter of the apse and presents, as is seen from the analyses, layers of plastering, prior to the painting, on which it is possible to find a thin pale imprimatur, with a tendency towards blue, probably used by the artist with the object of mitigating the lack of homogeneity of the surfaces before spreading the colour. The chromatic variety of the paintings was enriched by the use of gold, visible today above all in the splendid halos of the sacred figures, but which must have also originally affected parts of the painting, seeing that the recovery of various gold-plated fragments bring us to suppose a widespread use both on the figures and on the sky. The latter, realized in an intense blue, (artificial ultramarine) over a coat of blackish colour, appears to be, in fact, streaked by a multitude of golden ‘stars’, today unfortunately mostly darkened and hidden by the various repainting.
STATE OF PRESERVATION
The state of preservation of the paintings was very precarious. The major problem was represented by the diffused dusty quality of the pictorial film, which involved almost all of the colours, probably due to the progressive weakening and deterioration of the original tempera because of the notable presence of humidity in the environment and not only this. The flaking of the pictorial film turned out to be located only in particular areas or chromatic layers; some detachment of the layers of plaster were then noted, the latter located, above all, close to lesions which, especially in the left area, seemed to follow the state of the conch of the wall parameter demonstrating the exiguous thickness of the plaster.
The surface also appeared to be covered by dust and soot. The signs of previous restoring interventions were clear: two great restorations of the plaster are present in the portion of sky around San Lorenzo, besides various repainting which concern various areas of the painting, particularly the sky which, in the area to the right,(certainly that which shows the worst state of preservation), appears to also be absorbed in a thick layer of synthetic resin, probably used with the intent of blocking the dangerous pulverization of the colour.
RESTORATION INTERVENTION
► The restoration intervention on the paintings proposed to restore a sufficient compactness and stability of the pictorial film, seriously compromised, besides re-establishing the chromatic equilibrium which appeared altered by the bad state of preservation and by former restoration interventions.
► In the first instance we carried out the pre-consolidation of the pictorial surface through the use of acrylic resin in a watery emulsion in a low percentage (2,5%), sprayed directly onto the area to be treated and, after some minutes, padded with natural sponges on Japanese paper slightly dampened: without this generalized preventive intervention, any type of approach to the painting would have been made impossible by the extreme precariousness of the pictorial film. In parallel we carried out the re-adhesion of all the raised scales of colour through injections, on the back of the scales, of acrylic resin, and subsequent padding. The use of the acrylic resin was rendered necessary considering the high level of humidity of the environment.
► A methodology of cleaning was then studied which took into account the operational technique and, above all, the conservative particularities of the work in question by choosing in the end, a careful and accurate “dusting” of the surface by means of soft brushes of various dimensions: considering the impossibility of cleaning with water, however gently, this was, in effect, the only method which guaranteed us a satisfactory compromise between the aesthetic requirement and that properly conservative of the painting.
► In order to obtain a chromatically balanced cleaning of the sky which, given the differentiated state of conservation between the right area and the left one, represented one of the principal problems to be faced, it was necessary to remove the film of synthetic resin which, now modified, included portions of the blue, making it dark. A solution of acetone spread by a brush on Japanese paper, together with a light padding action was sufficient to bite into the film of resin, giving us back the brilliant colour of the blue.
► The golden halos of the Saints and of Christ, made opaque by dust and soot were, on the other hand, cleaned with small pieces of cotton soaked in a 5% solution of ammonia bicarbonate and alcohol.
► Before proceeding with the filling of the cracks and the consolidation of the plaster, a final reinforcing of the pictorial surface became necessary, in order to bring back the final cohesion to the colour, which allowed to carry out the subsequent operations with more safety: this was carried out again by spraying, with the use of acrylic resin in a watery emulsion in a variable percentage from 2 to 4%
► The stuccoing was carried out with mortar with a base of sand and slaked lime. The consolidation of the plaster and the wall support was realized with hydraulic lime PLM-AL with the addition of small quantities of acrylic resin (3%) to guarantee a better re-adhesion and for the necessity of a more solid anchorage, being a question of a painted vault; the superficial detachments, which involved the thin priming and the underlying layers of whitewash were, on the other hand, consolidated by means of injections of casein of calcium .
►The pictorial touch-up, carried out with mineral colours in powder and casein of ammonia, was effected veiling and reducing the tones: particular attention was paid to make the blue of the sky, which represented the main problem to be resolved, considering the different state of preservation from area to area, which disturbed the interpretation of the totality, as homogeneous as possible. The problem of the restoration of the plaster attributable to former restorations was also resolved in a pictorial manner.