Grave marker cleaning is by far the most common preservation effort that takes place within a cemetery. At Oakland, we have regular volunteer days focused on the task. When done properly, cleaning the headstones and monuments in a cemetery can make a fantastic aesthetic impact on the site. However, improper cleaning can lead to damage- both through mechanical and chemical means. In this blog, we will cover some of the most common mistakes that people make when cleaning headstones.
Using bleach: Bleach and Clorox contain soluble salts. When in a dissolved, liquid form, salt doesn’t cause much harm. However, when it crystallizes it expands and pushes on the crystals in the stone. Over time, this caused the stone to split or for outer layers to spall and disintegrate.
Using acid-containing products: Acid rain can cause great harm to a headstone over time and the same is true for cleaning products. Acids react with calcite (CaCO3) and break the molecules down. The products of those reactions depends on the acid involved but what is usually created is more easily washed away. This is called “dissolution” and is responsible for the gradual fading away of detail in marble headstones.
Cleaning unstable stones: Headstones are often very solid and strong-looking, but they are often not as stable as they appear. When you clean a headstone, you have to apply pressure as you scrub. If a headstone is composed of multiple pieces, you run the risk of knocking those pieces off their base. Further, thin, single-component grave markers are really fragile, and applying pressure can cause them to snap at the point where they insert into the ground. Failure to assess the condition of a grave marker in advance of cleaning can be disastrous!
Using wire brushes: Many stones are made of minerals, like calcite, that are considered “soft” on the Mohs Hardness Scale. Calcite makes up marble, which is the most common headstone material at Oakland. Soft minerals can easily be scratched with metal, so using a wire brush on a marble headstone leaves visible scratches. You might wonder, then, about granite. Granite is composed of many minerals, most of which are harder than a wire brush. However, one of the minerals that can give granite a “shimmer” is mica, which is even softer than calcite. So, no matter the stone, wire brushes are off limits!
Using Coca-Cola (yeah, I’ve seen people do this): Most soda products are acidic, so all the reasoning behind not using an acid-containing product applies here. Also, sodas have a boatload of sugar, which can make headstones attractive to biological organisms that feed on carbohydrates!
Want to learn how to properly clean a headstone? Join the Preservation, Restoration, and Operations Team on Monday, August 7 from 9-12. Contact email@example.com for more details.