The polychromed plasterwork of the Corral de Villalpando brothers. Historical study, scientific examination, conservation problems and possibilities of treatment

Abstract

Juan and Jerónimo del Corral, the former an architect and the latter a sculptor, developed their artistic activities in Castile during the second third of the sixteenth century. The originality of their work lies not only in their technique but also in their iconography: they combine the Spanish tradition of plaster work with the influence of the Italian Renaissance. This paper is a documentary and stylistic study of their work and discusses the problems of technique and conservation of the cupolas and walls of polychromed and gilded plaster relief. Due to its characteristics and its sensitivity to moisture, gypsum is a material which poses specific problems of behaviour and treatment. The various deteriorations it undergoes are shown as well as their causes and possible treatment. Scientific examination has been mainly directed towards the investigation of the support by IR and EDX spectrometry, the analysis of the polychromy by microscopy and the identification of the media by gas chromatography. The results show that the Corral brothers used a homogeneous technique for the plaster support, following the Hispano-Moresque tradition, whereas the polychromy shows various influences. As regards biological deterioration, two different groups of microorganisms were surveyed: bacteria and fungi. The results obtained in areas with and without polychromy and with various levels of moisture have been compared by different sampling techniques. Nitrifying and sulphate-reducing bacteria have been identified, which are responsible for the deterioration of stone monuments.