Sharing this blog post by the National Center for Preservation Technology and Training just posted today entitled: "Abrasive Cleaning of Grave Markers"
This article can also be accessed from the home page of the National Park Service.
Thanking Dr. Mary Striegel for answering my question in the post concerning the use of abrasive tools on gravestones such as "Nyalox Brushes"* that rotate on power drills used to clean and 'polish' the surface of a gravestone for inscription reading purposes, etc.; and often promoted for use in the name of restoring a gravestone to its original state.
No one is saying that these types of brushes do not have their proper place for an appropriate and effective use. In my opinion, a gravestone is not one of them. As this article points out, if you would not use this type of a power tool to clean "the surface of your automobile" ...."then you would not use it to clean a grave marker."
I encourage anyone who has questions regarding using any power tool on a gravestone to please devote a few moments to read this story, and consider that it is worth it to you and the gravestone to make the choice to use the least aggressive methods first -- methods that are non-invasive, non-toxic, and almost free!
For reading faint inscriptions on gravestones, try using mirrors ** to reflect sunlight on the names and dates.
If you feel you must clean, use plain water; it is recommended to use distilled water***.
Please review all of your options before taking even a scraper, or a brush, to a gravestone. Or, applying a chemical. Try the least abrasive and invasive techniques such as those mentioned above first. It will benefit both you and the gravestone with this approach!