Characterization of the binding medium used in Roman encaustic paintings on wall and wood

Abstract

The characterization by means of Attenuated Total Reflectance Fourier Transform Infrared Spectroscopy and Gas Chromatography-Mass Spectrometry of the binding medium present in eight samples of Roman wall paintings coming from three archaeological sites in Spain and a sample of a Roman-Egyptian mummy portrait on wood showed strong evidence that the medium in all the studied samples was composed of beeswax and soap. These results suggest for the first time that Roman artists used in wall and easel paintings a water soluble encaustic paint of beeswax and soap. Experimental studies with a wax-and-soap technique showed that this painting technique allows reproduction of the physical characteristics of many Roman-Egyptian encaustic mummy portraits with greater accuracy than the hot wax encaustic paint and the alkali-treated encaustic paint often considered to be the painting techniques used in these portraits. Wax-and-soap encaustic also showed greater accuracy in reproducing the physical characteristics of Roman wall paintings than the fresco painting technique, generally thought to be the technique used to execute such paintings. This study suggests that wax-and-soap encaustic could be a common painting technique among Roman artists, and its composition could correspond to a lost ancient encaustic formulation searched for the last five centuries by many artists and researchers dissatisfied with the former reconstructions of the ancient encaustic painting technique.