1 INTRODUCTION

IN RECENT YEARS, POULTICE CLEANING OF STONE SURFACES has become a popular way of gently cleaning the surface of unsightly accretions, dirt and coatings.1 The poultice medium serves to hold the solvent in close contact with the contaminating material for a long enough period of time to permit dissolution or swelling and adsorption into the absorbant material. The advantages of a poultice system include homogeneous application of the solvent and adsorption of the contaminant without risk of mechanical damage to the surface of the object. Attapulgus clay is often used as the sorbant material, because the particles provide a large surface area for solvent sorption and can be brushed away when evaporation is complete.2

More recently, colloids or gels have become popular as poultice media because of their high solvent to sorbent ratio.3 These gels are tangled masses of long chain polymers and liquid media, and can vary in viscosity from a fluid to a viscid solid. When solvent action is complete, the gel can be removed from the surface in a swelled or dry state. The gel is most effective as a poultice if the solvent is allowed to evaporate completely because the sorbed material or contaminants will follow the evaporation front and collect in the sorbing material.

Synthetic thickeners like methyl cellulose, carboxy methyl cellulose and hydroxy propyl cellulose have been frequently cited in the conservation literature for their use as poultice media, adhesives and consolidants. These polymers have found innumerable applications in industry as thickeners, binders, stabilizers, suspending agents, and rheology regulators in paints, inks, foods and cosmetics. Industrial applications for these materials have been expanded by the use of additives to plasticize, emulsify or insolubilize these products.

This paper will describe the use of a methyl cellulose poultice medium which was modified so that its properties as a gel and film former could be exploited in the cleaning of a work of art.