A cleaning method based on the use of agar gels: new tests and perspectives

For the peculiar artworks such as stucco plasterworks cleaning is troublesome for different reasons: weak mechanical behavior, high porosity and resulting water absorption, partial water solubility in the case of gypsum plaster. The choice of the cleaning method, especially as concerns gypsum based stucco materials, is crucial in assuring the lowest harmfulness possible together with a good level of efficacy. With the term agar we name a powder product composed mainly of polysaccharides and extracted from red algae species. When boiled with water, in a percentage range in between 0.5 and 5, it produces a colloidal solution that gellifies towards 35 °C. It can be used gelified and cold placed on a plan stucco surface, tepid and fluid poured on a surface relief or otherwise milled till a snow consistency, then pressed as a pad onto any surface; it has a high content of water which is slowly released into the porous substrate system. Hence the water-soluble components of soiling present on the surface are extracted and removed with the gel. Conservators should tune the following parameters to adjust the cleaning mode to a specific situation: agar powder concentration in water, application method (gel, tepid solution, "milled") and contact time. At the moment, agar gel is successfully used in cleaning gypsum plaster objects with grey coherent soiling deposits.In our study agar was used in cleaning a dolostone capital.