1. Never use wire brushes or metal instruments of any type. Never use such things as Pancake turners, Brillo pads, steel wool, Scotchbrite or any abrasive cleaning item.
2. We all have several types of cleaners around our homes, but almost all might harm a stone, especially the marble or limestone headstones. Never use acid or acidic cleaners. If these are used it should be only by conservators with proper training on non-calcareous stone.
3. Other types of cleaners we would find about our house that are bad are: all brands of soap, even Ivory, detergents, either liquid or powder, such as Borax, Clorox, TSP, Calgon, Formula 409, Spic & Span, Fantastik or any other abrasive cleaner, should never be used.
4. It is wise to make sure the marker is stable before you attempt to clean it. Check to see that there is no delaminating, flaking etc.If you find a stone which is hollow sounding when tapped with fingers, it is best not to do work on that stone at all.
Be aware that the use of improper cleaning materials and practices can cause serious and irreparable damage to the markers or gravestones, even though at the time they look wonderful to you now, years down the road, they will be worse than before you cleaned them.