The use of cellulose ethers in the treatment of polychromed surfaces

Pamela Hatchfield

Abstract

A variety of consolidants were considered for use in the treatment of Egyptian polychromed wood models in the collection of the Museum of Fine Arts. The results of earlier treatment of some of the objects in the collections with consolidants such as wax, hide glue, cellulose nitrate, soluble nylon, polyvinyl alcohol, and polyvinyl acetate emulsions were judged to be unsatisfactory. These materials altered surface appearance, attracted excessive amounts of dirt, usually contracted, embrittled and darkened on aging.

The Egyptians typically applied pigments in water-soluble gum binders. The use of very low quantities of these binders resulted in the matte, dry and unsaturated appearance seen on tomb models prior to treatment. These models are usually constructed of wood with gessoed and painted surfaces. Under conditions of changing temperature and relative humidity, the expanding and contracting wood substrate promotes disattachment and deformation of the gesso layer and painted surface. Many of these objects were treated with wax and other consolidants in the field. Others were treated with polyvinyl acetates, acrylic consolidants and even starches such as wallpaper paste. At best, these consolidants strengthened fragile paint films, although tented surfaces and misplaced fragments remained out of contact with the substrate. Aqueous solutions such as gelatine tended to stain and dissolve same painted surfaces before consolidating them.

Cellulose ethers were considered for use in the treatment of the tomb models because of their good aging properties and their versatile solubility in a range of organic and aqueous solvents. The use of cellulose ethers in organic solvents as a pre-consolidant strengthened the paint films sufficiently to allow the subsequent use of cellulose ethers in aqueous solutions. The subsequent use of aqueous cellulose ethers permitted manipulation of paint films back into contact with the substrate without dissolving or otherwise endangering the paint.

The structure and characteristics of some cellulose ethers will be described, as well as the reasons for choosing the Aqualon Klucel series and methyl cellulose as the cellulose ethers used to treat the Egyptian material. Case studies of several objects will be used as examples to illustrate the treatment procedure. Application of the technique to other water-sensitive materials will be discussed.