Today the 19th century concept of restoring is discredited. Restorers of stone sculptures need the assistance of art historians and historians of architecture, and knowledge of geology and analytical chemistry. The principles of restoration of stone carvings in museums and monuments are different. Inferior quality stones often decay almost beyond help. The limits of restoration are different in every case; it can be more thorough in monuments. In museum pieces restorations must be removable. The new part and the original must have the same hygroscopy, color, and structure. Other important guidelines are listed. See also 16-194. -- AATA