Here is an excerpt from a recent support ticket:
(Oh, and remember DO NOT USE BARKEEPER'S FRIEND ON ELECTRICALLY ETCHED MARKINGS - gal markings / logo markings)
Yes, beer stones are a pain. But there are solutions which are homebrewer friendly, they just take a bit more effort and time.
MoreBeer re-published a really good discussion on the problem, which offers several ideas on how to deal with it.
If your homebrew store doesn't have some of the chemicals, they are often available on Amazon or other online sources.
Please take a look at;
Hope that helps