To clean tombstones made of soft natural stone you will need plenty of water, buckets, natural bristle brushes and toothbrushes and non-ionic soaps or detergents. Please do not use wire bristle brushes or metal, acid, clorox, borax or pressure washers as these will damage the stones. The exception is Granite, limestone, sandstone or marble stones where you can use some more abrasive cleaners and pressure washers as long as the stone itself is in stable condition. I have never used a water pressure on the cemeteries which I have cleaned, simply because I do not wish to take the chance of losing information. Also, the engravings are to be considered. To remove calcium deposits in the engravings, a heavy duty non-metallic scouring paid should do it, then scrube it throughly with a detergent. For bronze stones, remember that they are mounted flat and so will holding standing water and debris.
These plaques already have a factory-applied lacquer coating to seal the appearance. Best to use the natural bristle brushes.
North Carolina Genealogy