A multi-analytical study of historical coated plaster surfaces: the examination of a nineteenth-century V&A cast of a tombstone

Valentina Risdonne,Charlotte Hubbard,Charis Theodorakopoulos,Johanna Puisto

doi:10.1186/s40494-021-00533-0

Valentina Risdonne, Charlotte Hubbard + Show 2 more

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https://doi.org/10.1186/s40494-021-00533-0

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Abstract

A multi-analytical study was designed to characterise historical coated plaster surfaces. The method was applied to investigate the surface coatings of the nineteenth-century plaster cast of the tombstone of the Presbyter Bruno that belongs to the Victoria and Albert Museum collection. At first, selected samples of the object were examined with Visible Light Reflectance and Ultra-Violet Fluorescence Optical Microscopy (VLR- and UVf-OM respectively) and Scanning Electron Microscopy (SEM) demonstrating a consistent stratigraphy featuring a bulk, an interface and an uppermost layer. The latter layer appeared to consist of an aged coating and dirt. Overpainted and repaired areas of the object generated samples that had additional layers on top of the aforementioned stratigraphy. A layer that seemed to be an additional surface varnish or a coating that had not been absorbed to the bulk has been observed in a couple of samples. Elemental characterization was carried out with energy dispersive X-ray spectroscopy (EDS) and further analyses were performed with X-ray diffraction (XRD) and Fourier-transform infrared (FT-IR) spectroscopy with focal plane array (FPA) imaging which confirmed that the bulk of the object is made of gypsum plaster containing mostly silicate and carbonate inclusions. Gas chromatography/mass spectrometry (GC/MS) and pyrolysis-GC/MS with extraction methods based on n-propanol followed by pentafluoropropionic anhydride (PFPA), tetramethylammonium hydroxide (TMAH) and 3-trifluoromethylphenyltrimethylammonium hydroxide (m-TFPTAH) were performed to detect organic media. The results suggest that the organic medium used for the surface coating is a diterpenic resin that contained silicon, aluminium and traces of other inorganic elements. The organic medium of overpainted areas was based on alkyd resins and the in-paints were characterised as a blend of silicon and barium at varied concentrations. This multi-analytical approach can generate a better understanding of manufacturing, component materials and conservation issues of coated plaster objects.

Highlights

This work represents a pilot case study designed to establish a wider campaign of sampling and scientific analyses of the surface layers of the casts produced in the nineteenth century, in the framework of a collaborative doctoral partnership of Northumbria University with the Victoria and Albert Museum (V&A) Museum (AH/R00322X/1) [1]
A sample of incoherent dirt and dust was taken from the base of the tombstone and a sample of plaster bulk was taken from a deep crack to confirm the expected composition of the substrate
Dust Dust deposited on the tombstone was sampled (Sample 1) and analysed to have a better understanding of the contaminants present in Gallery 46A, and eventually be able to discriminate which elements found on the surface can be attributed to the environmental dust in the galleries

Summary

Introduction

This work represents a pilot case study designed to establish a wider campaign of sampling and scientific analyses of the surface layers of the casts produced in the nineteenth century, in the framework of a collaborative doctoral partnership of Northumbria University with the V&A Museum (AH/R00322X/1) [1]. The object of this study is a nineteenth-century plaster cast of the Tombstone of Presbyter Bruno, part of the Victoria and Albert Museum (V&A) collection The ‘Copy of the Tombstone of Presbyter Bruno’ is a plaster replica of an original tombstone from the Cathedral of Hildesheim (Germany), by Friedrich Heinrich Nicolaus Küsthardt the elder (Göttingen 1830–Hildesheim 1900) [10, 11]. The original tombstone is dated 1194 and is still located in Hildesheim Cathedral. In 1873, the Museum acquired several plaster casts of key sculptural decorations in Hildesheim Cathedral, all produced by Küsthardt, among them, the tombstone, purchased directly from Küsthardt in 1873 for £6

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