While beautiful, over time, headstones or grave markers can get dirty due to the elements (snow, rain, dust, wind), bird droppings or even vandalism. Atmospheric pollution in the form of exhaust from automobile and industrial plants, acid rain, or airborne particles can settle on the surface of a gravestone and begin to deteriorate it. Cleaning a headstone can significantly improve the appearance of the grave and help preserve the stone.
Determine the type of stone. Marble, slate, soapstone, sandstone, limestone and granite have all been used to make headstones. A good reference for identifying types of gravestone materials is provided by Tracy C. Walther, architectural conservator for the Association for Gravestone Studies, in "How to Identify Major Stone Types." Bronze is often used for plaques mounted on a concrete or granite stone base, and there are some monuments completely made of brass.
Identify the type of material or soiling that you are trying to remove. Tracy C. Walther classifies these as: Carbonaceous or sooty material (deposited by car exhaust, dirt in the air);Organic (algae, fungi, lichens, mosses);Stains (metallic, oils);and Efflorescence (from salt in the air, common in areas by the ocean). Another category is paint, caused by vandals spraying graffiti (consult with a chemical cleaning company about removal).
Select your cleaning agent. The Association for Graveyard Studies recommends beginning with a mild, non-ionic detergent and water. These are available from conservators' or photographic supply houses. Household ammonia may be effective on marble and limestone (mix a 1 to1 ratio with water). Calcium hypochorite (used for disinfecting swimming pools) can be used for removing organic (plant) growth; mix 59.1ml. dry to 1 gallon warm water. Commercial household detergents (liquids or powders) are not recommended for cleaning because, according to Tracy C. Walther, "...they are rendered insoluble by calcium ions present in stone and hard water. They may also produce free alkali and fatty acid salts." Pour the cleaner into a spray bottle for easy application. According to James R. Walker, metalsmith, paste wax or a non-ionic soap like Ivory will work well on brass markers or nameplates.
Remove loose dirt and other dry materials from the stone with a soft-bristled brush. Never use a wire brush or sandpaper, as these can scratch or otherwise damage the stone.
Put on your rubber gloves and goggles for protection. Test your cleaning agent on a small, inconspicuous spot on the stone. This will let you know if your agent is too harsh (the stone turns colours, starts to bubble, smoke, melt or looks worse) and it will give you an idea of the results you can expect from the overall cleaning.
Wet the entire stone with clear water. Begin scrubbing with a soft-bristle brush. Rinse with clear water.
Start at the bottom of the stone (to prevent staining from streaks running down from the top), apply the cleaning solution with a spray bottle (make sure you have goggles and rubber gloves on). Work on a small area, brushing gently after your spray to remove soil and grime. Use a cotton swab to clean inside recessed areas like letters, numbers and carved images. If the swab is too soft to remove the grime try a small stick, but do not gouge or scratch the stone.
Rinse off the cleaning agent before it dries with water. If the cleaner dries it will be harder to remove, and permanent staining or streaking could occur on the stone. Move on to the next adjacent area, spraying, brushing and rinsing as you go.
Depending on the results of your initial attempt, clean again using a stronger cleaning agent. Know when to stop cleaning;overzealous cleaning can damage or break very old stones.
Take all your cleaning agents, tools and used rags with you when you leave the grave.
Use an eco-friendly cleaner. A completely natural, nondestructive method for cleaning biological plant material (moss, lichens, fungi, algae) from gravestones based on research in Newfoundland cemeteries involves using snails. Place standard garden snails on the tombstone and let them go to work.
Know when to call in a professional. A local historical society, preservation group, university, museum or cemetery office can direct you to persons with the advanced skills, knowledge and equipment to perform tough cleaning jobs.
Serious damage can be done to stones by the use of improper cleaning methods. The Association for Grave Studies and Gravestone Preservation info suggest NEVER using the following: sandblasting, wire brushes, acidic or acid-based cleaners (especially on marble or limestone), bleach or household cleaners, or high-pressure spraying. And, products like Fantastic or TSP are too abrasive; chlorine bleach is not recommended as it also contains salts.