Widespread stone cleaning of Scottish buildings began in the 1960s. In the earlier years, abrasive cleaning caused significant damage, especially to sandstone buildings, abrading the stone surface and blurring detail. Chemical cleaning systems avoided these problems, but could cause staining or bleaching; inevitable chemical retention within porous stone resulted in the formation of potentially damaging salts. Recent years have seen the development of considerably less damaging cleaning systems, but the legacy of previous cleaning interventions remains. Stone cleaning has often resulted in increased rates of decay on stone façades, with considerable long-term repair costs. 12 refs.