Ochre-Based Pigments in the Tablinum of the House of the Bicentenary (Herculaneum, Italy) between Decorative Technology and Natural Disasters

Michele Secco,Ivana Angelini,Francesca Piqué,Kiernan Graves,Leslie Rainer,Gilberto Artioli,Arlen Heginbotham

doi:10.3390/min11010067

Abstract

Ochre-based pigments have been employed since the first artistic expressions of mankind, with widespread diffusion during the Roman civilization. Such prominent use influenced their technological development, focused on functional and aesthetic optimization through complex manufacturing procedures. Furthermore, their appearance is also influenced by degradation processes, sometimes driven by natural disasters such as the eruption of Mount Vesuvius in 79 AD, in which yellow ochres of Vesuvian sites were sometimes converted to red by thermal alteration. In this contribution, a multi-analytical approach was adopted based on preliminary non-invasive investigations complemented by laboratory analyses to characterize the painted surfaces of the tablinum of the House of the Bicentenary (Herculaneum) with a particular focus on the ochre-based monochrome backgrounds. The study was aimed at (a) reconstructing the original color scheme of the walls and (b) deciphering the complex decorative techniques adopted by Roman craftsmen. The analytical results allowed testing and defining analytical procedures for the discrimination between the original and converted red pigments. Furthermore, these studies indicated that specific decorative technologies were adopted according to aesthetic, functional, and economic purposes, including the utilization of various qualities of ochre with different compositional and textural properties, and the mixture of ochre pigments with other compounds.

Highlights

IntroductionRed and yellow ochres constitute by far the most widespread and extensively used class of mineral pigments since the beginning of the artistic expression of humankind, being among the earliest pigments used from the Paleolithic era, and later in Egyptian, Persian, Greek, and Roman art, up to the Byzantine, Medieval, and modern period [1]
Iron and calcium were the dominant elements detected, with iron likely related to the chromophore compounds of the ochre-based pigment dispersed in the paint layer, and calcium mainly deriving from the lime-based binder and marble aggregate of the underlying plaster, apart from the sample sites showing high levels of S, where part of calcium should be attributed to the occurrence of secondary gypsum, widely observed in the tablinum walls as superficial alteration product [18]
The analytical campaign on the painted surfaces in the tablinum of the House of Bicentenary made it possible to answer the main archaeometric questions formulated at the beginning of the study, namely, (a) to determine the original decorative scheme of the red and yellow-painted backgrounds of the tablinum, heated by the pyroclastic surge of the eruption, and (b) to characterize the compositional and textural characteristics of the painted plaster sequences, determining the nature of the ochre-based pigments used for the fresco-painted monochrome backgrounds

Summary

Introduction

Red and yellow ochres constitute by far the most widespread and extensively used class of mineral pigments since the beginning of the artistic expression of humankind, being among the earliest pigments used from the Paleolithic era, and later in Egyptian, Persian, Greek, and Roman art, up to the Byzantine, Medieval, and modern period [1]. Hematite and goethite constitute the most common chromophore phases in red and yellow ochre, respectively They are generally associated with accessory silicate minerals like clays, quartz, and feldspars, whose amount and composition are mainly related to the source of extraction and processing of raw materials [2]. Ochres are characterized by exceptional aesthetic and technological properties, such as good pigmenting properties and relatively high chemical and physical stability, favoring their application on a wide range of organic and inorganic substrates and employing a wide variety of binding media [2]

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Discussion

Conclusion