My folks have had a few old farm houses in France over the years. Lime stone means that they're pretty unforgiving when it comes to old soot stains, but the softness means it can usually be blasted off.
But like you said there are some spots, like where an old chimney ran, which just don't clean.
There was a lot of belly scratching from the stone mason at the time saying none of it would come out and they should plasterboard. But in the end most if it came clean and the bits that didn't just looked characterful.
My folks have had a few old farm houses in France over the years. Lime stone means that they're pretty unforgiving when it comes to old soot stains, but the softness means it can usually be blasted off.
But like you said there are some spots, like where an old chimney ran, which just don't clean.