Kory Berrett, Virginia Naude and Richard Wolbers
This paper describes a recent treatment project that succeeds in providing deep cleaning of stained marble where traditional methods had failed. The treatment methodology builds on poulticing techniques using an aqueous cleaning system delivered with a gel-paste poultice mixture. Two materials new to conservation are introduced: a gelling agent, Vanzan NF-C, that is especially effective for aqueous media and can tolerate an unusually wide pH and ionic strength range while maintaining high viscosities; and nitrilotriacetic acid (NTA) a chelator for calcium ions able to disrupt relatively insoluble calcium salts, and staining agents formed by residues of prior treatments (detergents, soaps, coatings, etc.), without affecting the calcium carbonate itself. This new approach promises to be useful for similarly stained marble sculpture.