1 INTRODUCTION

Conservators have adopted commercially available products into their repertoire of treatment materials for filling nonstructural small losses in selected objects made of ceramics, wood, and mixed media; sculpture; and paintings. This category of fill material has not received the same scrutiny and testing that traditional fillers, varnishes, paints, and adhesives have. The following information has been gathered primarily from the Material Safety Data Sheets (MSDS) listed in Further Reading, the manufacturers' technical representatives, and, when available, conservation literature. Review of the information is intended to aid the conservator in selecting a fill material.

The general advantages and disadvantages of commercial vinyl and acrylic fillers versus traditional fillers are compared. Discussions of acrylic modeling pastes and vinyl-based fillers are accompanied by working characteristics of specific products. A chart has been compiled listing composition, pH, odor, and specific gravity from the MSDS and working properties such as gloss, color, texture, and the ability to sand, solvent finish, or burnish, gathered from the authors' practical experience and manufacturers' directions. Myriad products are available through the construction and the arts and crafts industries; no attempt is made to be exhaustive. The products were selected by availability from conservation supply companies, by references in recent books on repair of ceramics, and by familiarity to the authors.

Commercial vinyl and acrylic fill materials offer greater convenience and flexibility in application than traditional gap-filling materials, including plaster, gesso, and oil-based putties. These ready-mixed fillers consist of vehicles or binders, bulking agents, and additional agents, such as thickeners, foaming agents, emulsifiers, pigments, and biocides. The vinyl-based products, which are intended for patching or spackling plaster or wallboard, have been adopted from the construction industry, while the acrylic products were developed for artist and craft uses. None of the commercial products commonly used in treatments was developed specifically for conservation usage, with the exception of the new BEVA Gessoes, which were introduced in January 1997. Full disclosure of contents and consistency in composition over time cannot be assured. Many of the ingredients are trade secrets, and formulations change repeatedly without notice.