Porous impure limestone containing a high concentration of clay minerals is highly susceptible to decay even in a museum environment. Hanna briefly outlines the reasons for decay within a museum -- relative humidity, acid gases in the atmosphere, airborne dirt, dampness -- and the measures available to prevent decay from happening -- environmental control, consolidation -- before presenting a British Museum case study of the treatment of a lifesize Egyptian limestone head of Amenophsis 111 (1417-1379 BC) using silane-based consolidants. See also 21-1334 for reference to entire proceedings. -- AATA