When I was first learning archaeological lab techniques for handling artifacts, I was told, and rightly so, that cleaning, even if done carefully, was likely to remove more than “dirt,” and whatever else got removed might be significant.
If you can follow that run-on sentence.
I have to laugh at some of the reactions to the “Chroma: Ancient Sculpture in Color” exhibit at the MET in NYC. It includes Greek and Roman sculptures that we almost always see in naked marble or other material, as if they were not painted when originally displayed…even though the fine art professionals that put them on display and analyze them know darned well that paint flecks are still embedded on their surfaces.
Without a doubt, they were painted. And painted brightly. Take a look…wait, here’s an example. This is “Reconstruction of a marble finial in the form of a sphinx” by Vinzenz Brinkmann (link).