Surface orange patinas on the limestone of the Batalha Monastery (Portugal): characterization and decay patterns

Yufan Ding,Nick Schiavon,Emma Angelini,José Mirão,Pedro Redol

doi:10.1007/s11356-021-15490-1

Abstract

Samples of orange patinas found on a limestone window tracery and an ornament of the Batalha Monastery have been investigated by X-ray micro-diffractometry (μ-XRD) and low-vacuum scanning electron microscopy coupled with energy dispersive spectrometry (LV-SEM + EDS). The aim of the study was to determine the composition of the layered patinas, assess whether they have been intentionally applied or naturally formed, and study their degradation patterns. Preliminary results revealed that the orange patinas on the window tracery and the ornament showed different compositions and appearance, suggesting distinct formation pathways. Orange patinas on the ornament, which are now showing decay and delamination patterns, mainly consisted of gypsum with hematite as a minor component, implying the possibility of an intentional application of a mixture of ochre and lime as tint plaster. Orange patinas on the window tracery show, instead, the presence of Ca-oxalates, abundant weddellite, and minor whewellite, with minor hematite suggesting the yellowish/orange color as being due to Ca-oxalate patinas imbedding soil dust airborne particles. Such patina was possibly formed naturally either by the chemical attack due to atmospheric air pollutants from traffic exhausts emissions or by bacterial activity. No delamination was observed on the window tracery sample with granular decohesion as the major decay phenomenon. A comparison was made between this patina and the so-called scialbatura, a surface yellowish coating often found by conservators on limestone and marble in ancient monuments in the Mediterranean region.

Highlights

The famous Batalha Monastery located in the small town of Batalha in Central Portugal was built and restored using Jurassic oolitic limestones extracted from several quarries in the region surrounding the monument (Aires-Barros 2001; Ding et al 2019)
The statue showed the presence of calcite with minor nitrate, silicate, and organic products like benzoic acid, while on the external walls, the orange patinas were found to be predominantly composed by calcium oxalates such as whewellite (CaC2O4·H2O) with minor weddellite (CaC2O4·2H2O), together with hydroxyapatite (Ca5(PO4)3(OH)), halloysite, and nitrates (Aires-Barros et al 2001)
These results suggested these patinas to represent what conservators called “scialbatura,” e.g., a superficial film present as a surface coating on calcareous Greek and Roman monuments in the urban areas, colored variously yellow, brown, pink, or red and often associated with pitting phenomena (Lazzarini and Salvadori 1989)

Summary

Introduction

The famous Batalha Monastery located in the small town of Batalha in Central Portugal was built and restored using Jurassic oolitic limestones extracted from several quarries in the region surrounding the monument (Aires-Barros 2001; Ding et al 2019). Portugal 4 Department of Geosciences, University of Évora, Évora, Portugal monastery limestone is extensively covered with orange patinas which can be seen on the surface of facades, ornaments, columns, and walls (Fig. 1). Few studies on this subject can be found in the literature. The statue showed the presence of calcite with minor nitrate, silicate, and organic products like benzoic acid, while on the external walls, the orange patinas were found to be predominantly composed by calcium oxalates such as whewellite (CaC2O4·H2O) with minor weddellite (CaC2O4·2H2O), together with hydroxyapatite (Ca5(PO4)3(OH)), halloysite, and nitrates (Aires-Barros et al 2001)

Objectives

Methods

Results

Conclusion