Materials and Techniques for the Coating of Nineteenth-century Plaster Casts: A Review of Historical Sources

Abstract

This review paper offers a summary of historical techniques and materials used to produce plaster casts and to treat their surfaces, as found in the historical literature. It reviews a selection of manuals, treatises, and recipe books on the art of the cast makers as well as a selection of patents related to the manufacturing of casts and the coating of their surfaces. The introduction to the review shows how relevant archival, historical, and technical investigation demonstrates that nineteenth century replicas are works of cultural significance in their own right, by means of a synthesis of background information. This paper also offers a brief introduction to plaster moulding and casting as well as a summary of historical recipes on how to treat the surfaces of plaster casts to change the surface properties or their appearance. This review aims therefore to provide a summary of materials used by the nineteenth-century plasterer, and technical information for the use of conservators, researchers, and curators who engage in the care and study of historical plaster casts. Examples from the Victoria and Albert Museum's collection support the information found in the historical literature.

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

“…Al is likely present, together with potassium (K) and silicon (Si) as part of silicate inclusions (visible in the EDS mapping and spectra, Fig. 7), which constitute clay minerals [47] and are reported to be present as a natural contaminant of mineral gypsum [2,48]. FT-IR spectra suggest vibrations in the 950-1100 cm −1 region, characteristic of clay minerals (Si-O containing minerals, such as kaolin, Al 2 Si 2 O 5 (OH) 4 ) [40,47].…”

“…Megens et al [20], on the other hand, have demonstrated that systematic elemental analysis is required to uncover the provenance and composition of plaster used to replicate art and decorative objects: traces analysis, size and distribution of porosity and mineral shape and growth can be characteristic of a particular group of artefacts. Gypsum plaster (calcium sulfate, CaSO 4 •0.5H 2 O) has consistently been found as the main component of the bulk of the nineteenth-century plaster casts [2]. However, organic (such as resins and gums) and inorganic compounds (such as clay, sand, lime), as well as larger structural elements (such as fabrics, wooden or metal batons or even bones) were combined and added during the plaster production, as used to improve mechanical properties, such as hardness and water resistance or to control setting time and the casting procedure [2,20].…”

“…Gypsum plaster (calcium sulfate, CaSO 4 •0.5H 2 O) has consistently been found as the main component of the bulk of the nineteenth-century plaster casts [2]. However, organic (such as resins and gums) and inorganic compounds (such as clay, sand, lime), as well as larger structural elements (such as fabrics, wooden or metal batons or even bones) were combined and added during the plaster production, as used to improve mechanical properties, such as hardness and water resistance or to control setting time and the casting procedure [2,20]. The complexity of the organic and inorganic blended compositions in the plaster artefacts suggests that a multi-analytical approach would be more appropriate.…”

“…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]. Part of the project focused on the characterisation and the ageing characteristics of the original coatings of historical plaster casts [2]. In the nineteenth century, the plaster cast replicas of famous artworks were used extensively in schools and museums [3][4][5].…”

“…The lines have been sanded down, suggesting the cast could have been made using a piece mould technique. Piece moulds tend to leave raised seamlines on casts and, they were often disguised by sanding them down [2].…”