If in doubt, don't clean an old tombstone.

Cemetery headstones and memorials should be cleaned no more than once every 10 years. Even then, there are things you should and shouldn't do when tidying up the tombstones of your loved ones and ancestors. Arrive at the cemetery with the right knowledge and the right cleaning supplies.

Assess the condition of the stone you want to clean. If the headstone is in bad disrepair, it's best not to clean it. If the stone is flaking or brittle, cleaning will make it worse. Don't clean headstones that are cracked or that sound hollow when you rap on them with your knuckles. Such stones aren't sound enough for cleaning.

Avoid trying to correct certain conditions. Never clean a wooden marker; the wood could be rotted beneath the surface and cleaning could cause breakage. You can clean cast iron headstones the same as stone monuments, but do not try to scrape away any rust or flaking metal. Avoid removing moss, fungi, lichens or other algae growing on the headstone. Cleaning natural growth often causes more damage to the marker than leaving it alone.

Wet the headstone thoroughly. Use only natural spring water or rain water. Purchase several bottles of spring water for the job or save rain water beforehand. Do not use hard water, which can damage the stone due to mineral content. If you must use a recommended cleaner on the headstone, be sure you have plenty of water for rinsing the stone.

Clean the headstone only with a soft-bristled brush. Do not use brushes with natural bristles, which can stick to the marker's surface and promote natural growth. Bristles also should not be dyed; white nylon bristles are ideal. A soft, white toothbrush is safe for gentle cleaning of inscriptions and other detail work.

Stick to biodegradable, non-ionic cleaners if you must use a cleaning solution. Progenealogists.com, the website of a consortium of professional genealogists, recommends Orvis, used to clean horses and available at tack or feed stores, and Photo-Flo, sold at photographic supply stores. Rinse with plenty of water. Never allow cleaners to dry on a stone or stand too long.