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

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.

The Victoria and Albert Museum Plaster Casts by the Nineteenth-Century Workshops of the Notre-Dame Cathedral: Scientific Analysis and Conservation

“…Before being stored in vials, the samples were numbered with the museum accession number and progressive sampling numbers, which are used throughout the study to identify the samples as follows: MUSEUM ACCESSION OBJECT NUMBER_PROGRESSIVE SAMPLE NUMBER. A summary of the samples' locations and descriptions can be seen in Figure A1 and Table A1, and more details can be found in the databases available in the online repository [22][23][24][25].…”

“…The objects were also rendered in Autodesk ® AutoCAD ® 2019 for mapping purposes (Figure A1). Full photographic and AutoCAD ® documentation can be found in the databases [22][23][24][25][26].…”

“…Samples from the plaster casts were taken from pre-existing areas of loss to investigate the stratigraphy and the method of manufacture. A summary of significant scientific results is shown in the following pages and the full database of analysis is available in the online databases [22][23][24][25][26].…”

“…A summary and description of the samples, layer by layer, can be seen in Table A3, and a full record is available in the online database [22][23][24][25][26]. Table 2 presents a summary of the results by object.…”

Cleaning testing of nineteenth-century plaster cast reconstructions with thin polyacrylamide-based surface attached gels

“…The reconstructed gypsum plaster plates were based on the materials characterized on 12 V&A plaster casts produced in the nineteenth century by the Küsthardt, Notre-Dame and Franchi workshops [20]. Multianalytical studies [21] characterised the materials and revealed the simple stratigraphy of the selected casts, made of gypsum plaster and coatings [20][21][22][23][24]. In line with historical treatises [25] organic coatings such as shellac resin, linseed oil, beeswax and inorganic coatings such barites were identi ed in the original casts [21].…”