So, you've just finished scraping off the lichen and scrubbing the gravestone with water. Now it's time to apply D/2 Biological Solution to kill the lichen and whiten the stone. You spritz some on the damp gravestone and...oh no! Why is the gravestone turning pink?! Don't worry--sometimes stone will turn a subtle color of pinkish-orange after applying D/2 Biological Solution. The manufacturers of D/2 explained it to me that the color change is the result of the biological organisms reacting to the D/2. This temporary discoloration can take on shades of orange, pink, or gray. Not all stones react this way but some will. When it does, it will generally take 24-48 hours before the discoloration disappears. So, the only downside is that you may have to come back after a few days to take some good "after cleaning" pictures.
Here in Wisconsin we've had a very hot summer...we're talking about several days in the 90s with heat indices over 100. Should you clean gravestones in such extreme weather? When it comes to cleaning dark colored gravestones, the answer is "probably not."
I'm not even addressing the fact that doing any physical labor when it's that hot outside is dangerous here. I'm just addressing a question I get about cleaning gravestones during extreme weather.
The type of gravestone you should avoid cleaning on hot, sunny days are the black, granite ones. These are the grave markers that are hot to the touch. If this is the case, you should NOT clean them. Why? According to Jason Church, materials conservator, for the National Park Service (NCPTT), the liquids you are using to clean may react with the surface finish of the granite, permanently damaging it. No one wants that to happen. Remember our guiding principle when cleaning gravestones? Do no harm to yourself or the grave marker.
What about light colored gravestones or those which are non-granite? I would suggest avoiding cleaning those too if they are hot to the touch. Just wait for a cooler time of day or for a more mild day.
Jarrod Roll...museum curator by training, preservation educator by passion. Director of the Monroe County Local History Room & Museum, Sparta, WI. Owner of Save Your Stones Gravestone Restoration Services. Maker of the Gravestone Cleaning Kit.