Cleaning a granite fireplace

[Cornish Restorer]

Restoring a granite fireplace which had an open grate in it. Hoping to line the chimney and install a small log burner but would like to clean the blackened stone interior. Not sure if it’s from coal or wood but can’t shift it with soap and water. Does anyone know what might work please? Thanks

 

[Glenn586]

Sounds like it might be a whole lot of pain trying to get that clean enough for show. I'm sure sand-blasting would work but get ready for the mess. Might be worth looking at going over the top with brick/stone slips.

 

[Stevers]

Caustic Soda mixed according to instructions with appropriate protective gear might shift it.

I used a relatively weak mix of it to remove paint and soot from a my Doulting (Oolitic Limestone) fireplace.