Characterization of pigments used as protection and decoration on exterior facades of historic buildings

Abstract

All historical periods have their own specific characteristics and the color of the buildings is one of them, which can be present in the plaster or as a component of the substrate material. Originally, the plaster and coatings in buildings had a double mission: to protect and to decorate the walls, while nowadays, more importance has been given to the decorative aspect than to the protective function. From the end of the 19th century, with the appearance of the petrochemical industry, the use of natural pigments and binders was minimized and industrialized paints with artificial pigments were produced. The time and the different interventions suffered by many of the historic buildings, cause the loss of information of relevant importance in the conservation of historical heritage, significantly affecting the color, which has been eliminated or has disappeared hidden under layers of paints of later times. Thus, the objective of this research was characterization of painting layers superimposed on exterior facades and determination of their function in a late 16th century house located in the Colonial City of Santo Domingo, Dominican Republic. In order to revealed the history and composition of the original painting layers optical, mineralogical and microstructural characterization of the facades, techniques based on non-destructive (UV-vis spectrophotometry, Raman) or semi-destructive (X-ray diffraction, Scanning Electron Microscopy) methods have been used. Based on the comprehensive characterization of the 16th century painting layers, identification of one green and three red pigments was done. It was concluded that one of the red pigments had a role of waterproofing and biocide material, with the dual function, as a colorant and protective antimicrobial material.