Primary stabilization factor of the corrosion of historical glasses : the gel layer

Leached gel layers of variable thickness and composition, mostly crisscrossed by cracks and fissures, are built during long-term exposure of historical glasses. Depending on the glass composition as well as on the environmental conditions the gel layers show various shapes. They can be characterized by microprobe investigations, through photographs of the cross-sections in vertical plane to the corroded surface as well as determination of the chemical composition. Any cleaning measures in the course of restoration have to obey carefully their preservation, for it seems quite reasonable to assume that the progress of corrosion of the poorly resistant glasses is remarkably retarded by silica gel barriers.