If you spend any amount of time wandering through cemeteries, here is some of what you might want to know about cleaning headstones.  All this information courtesy of good friend and fellow genealogist, Patrick Lengyel, Professional Geologist (i.e., he knows a lot about rocks).

First, what headstones are made of:  you might see some trends if you stop to recognize them.  White sandstone headstones tend to develop the least amount of lichen because they are mostly quartz and there is nothing for the lichen to eat.  Marble gets a little more lichen, because the calcium in the calcium carbonate is digestible.  Pink granites tend to get the most lichen and sooner because they are full of potash feldspar, and the potassium breaks down and is even more digestible than the calcium in marble.  Black granite is less so because it is mostly calcium, feldspar, and amphibole.  You might think the calcium feldspar would be attractive like calcium carbonate, but carbonate is much easier to break down with weak acids, feldspar less so.

The only accepted cleaning agent for headstones and monuments is a biological product named D/2 (see www.gravestonecleaner.com).  Never use any chemicals on headstones.  If the headstone is quite bad, use water first to get the worst off, then apply D/2.  Always use a medium to soft plastic brush, like a dish cleaning brush.  

You MUST NOT use bleach or any chemical other than D/2 or it destroys the stones.  Buy a good quality garden sprayer and take a 5-gallon bucket of water with you because not all cemeteries have water access for the public.  The sprayers are better than just splashing it on because they spray in a fine mist rather than a big pour.  The trick is to get the lichen wet and keep it wet, so it gets soft.  The fine spray allows the water to last longer, something that may be important if your cemetery is in the middle of nowhere.  But even wet, lichen can be hard to remove.  Plan on spending 1 to 2 hours for a headstone with a lot of growth.  Spray, scrub, rinse, repeat.  Even with the D/2 product, I suspect you’ll have to take the bulk of it off with water and elbow grease and then use D/2 at the end. 

Good luck!  And be prepared to discuss your efforts with cemetery inhabitants (visitors and caretakers) since many might not understand the science behind your process.

Ron Gilmore

Email:    rvg3@me.com

Website:       https://rgenealogy.ca