In our inglnook we had soot stained bare stone and bricks. I tried scrubbing it, but enough perstsists.
I did read somewhere that cow dung helps (I suppose it absorbs the soot ??), but that wasnt an option for us.
I eventually Lime-rendered, then lime-washed (white - not a good idea), but that just adds water and it seeps through
We eventualy had to revert to painting with red limewash to hide it...looks great actually
I left all the soot in my fireplace and installed a woodburner in front of it. It's a bit black in there but I quite like it that way. Gives an indication there was once a proper fire there with a leaky smoke hood. I asked the other half over dinner tonight and without any prompting either way she said she appreciates it too. Just a thought as it would be a hassle to get those lovely years of soot back.