Is there something I can use to remove the stain.

My husband and I are renovating a house built in 1897. We have a stone
fireplace, that we believe to be slate or granite. It had multiple layers of
paint on it which we have stripped, but the final layer seems to be a black
stain. I can not find any references to anytime of stone stains. I was
wondering how If there is something I can use to remove the stain. Rubbing
it with the paint thinner helps some, but I would like to get it to an even
color if possible.

Kim