Makes me cringe and remember the Elgin marbles. I would hope they will be VERY professional about it and try it out on a little tiny piece first... or on a piece of the same marble dating from the same period if that's available. My brother in law restores art and is very careful that way but boy, have we seen restauration horrors in some of the 19th century paintings we find. And, of course, every person who cleans a painting insists he does it right. Oh my, this is giving me a very bad feeling. Very bad indeed!