I think I got this info on this forum but waaay far back in time, and it worked so well I wanted to celebrate with another post. I have a natural stone fireplace with large hearth, the stones are different types, colors, textures, etc and not "smooth". The former owner had daily fires and never cleaned. How to get off 20 years worth of soot? Over cleaner! I let it sit about 20 minutes and then scrubbed off with a white nylon pad, rinsed with water. An amazing amount of soot came off, far more than I had loosened with soap-and-water, which was my first effort. If ya think about it, carbon in an oven and carbon on a hearth aren't that much different, as carbon goes. So THANK YOU to whoever put the oven cleaner post up previosly.