Brief explanation of abrasive cleaning methods, how they can be physically and aesthetically destructive and way they are generally not accepted as preservation treatments for being responsible of damage to building materials. Alternative methods are mentioned, however, it would be impossible to state definitevely which of these will be the most effective. There is no formula that will be suitable for all building surfaces and, meantime, cleaning must be approached with caution through trial and error, using the gentlest means possible . -- ICCROM