New Methods of Applying Rigid Agar Gels: From Tiny to Large-scale Surface Areas
Ambra Giordano, Paolo Cremonesi
Abstract
Agar, a natural polysaccharide, has gained increasing popularity among conservators worldwide in the past two decades as a gelling material for water and aqueous solutions. Converting the aqueous medium into thermo-reversible hydrogels enables cleaning and humidification treatments to be performed with very strict control of the amount of water released. Even sensitive surfaces of different types of artworks can thus be treated with a good degree of selectivity. When the surface possesses sufficient cohesion and is compatible with a temperature of approximately 40°C, the semi-solid state of the agar gel represents the ideal means of application. From a practical point of view, however, restricting the application to limited areas may be difficult; furthermore, a homogeneous application to large areas may be even more problematic: in this near-solid state, the gel remains workable for only a short time. This contribution addresses both situations by introducing specific tools and the related methodology to treat both very small and large areas. A heated syringe-pistol can be easily assembled for the former situation, and a commercially available paint sprayer can be used for the latter. This novel spray application has been considered in detailed studies. It produces a flexible, ductile film with quite a different morphology from that of the film traditionally produced by warm application and cooling. The syneresis process is thus affected by the different gel structure. The extremely controlled release rate of water from a spray-applied hydrogel makes this application highly compatible with even the most sensitive surfaces.