Seeing Clearly: Casting Epoxy Fills for Glass Objects Using Transparent Molds

Rebecca Gridley and Karen Stamm


This paper focuses on the use of transparent molds for casting large epoxy resin fills for glass objects. It presents two treatment case studies that employed different mold-making techniques and materials: clear silicone rubber and vacuum-formed polyvinyl chloride (PVC) foil. In each treatment, the fill or replacement piece was cast separately from the object in order to minimize handling or protect sensitive surface decorations. The materials discussed can also be applied for casting epoxy fills in situ. Two Austrian “façon de Venise” (style of Venice) glass vessels from The Metropolitan Museum of Art’s collection were recently treated in preparation for display. These blown glass vessels are ornately decorated with diamond-engraved patterns and passages of gilding, paints, and translucent glazes (so-called “cold paint” decorations, applied after the glass had cooled). Both vessels retained major restorations, which had either aged poorly or were fashioned from visually unsympathetic materials, rendering them unsuitable for exhibition. The restorations compensated for significant losses: more than a third of the rim of the larger vessel is missing, and the smaller vessel has lost its foot. The latter had a 19th-century plaster replacement foot, which itself was in poor condition and was not representative of the vessel’s original profile. The presentation will focus on the practical challenges of casting large epoxy resin fills and replacement pieces for these objects. It will also touch briefly on the decision-making process that led to the re-restoration of these objects and the discussions about the extent to which the restorations should be integrated. Casting transparent epoxy fills for glass objects is particularly challenging, in part because of the high level of finish required. Transparent mold-making materials allow the conservator to monitor and prevent internal flaws that develop during the casting process. This is a critical level of control, as the entire cross-section of the epoxy fill remains visible in the final product. To cast a new foot for the smaller vessel, a traditional two-part mold was made using P4, a platinum-catalyst silicone rubber by Silicones Inc. that cures water clear. The treatment of the larger vessel included the experimental use of a double-walled transparent polyvinyl chloride foil mold. This material was introduced to glass conservation practice by Gorazd Lemajič and the forming technique was developed in collaboration with Met conservators (see Lemajič 2006 and Stamm 2013). This case study presents a novel use of this technique to cast fills separately from the object rather than in situ. In each treatment, preparatory steps and material selection minimized or eliminated the need for laborious hand-polishing to recreate a glasslike surface. The presentation will conclude with a discussion of the advantages, drawbacks, and potential applications of the materials and techniques used in these two treatments.

2019 | Uncasville | Volume 26