I have been asked to restore a fire place mantel or surround. Please see attached picture. The stone has been removed from the wall and is currently dismantled. My plan of attack was to 1st poultice it with 40 % hydrogen peroxide before using honing pads to remove any surface etches. My question is, is there any potential problem in applying the peroxide poultice? Or do you have any other recommendations to brighten up the stone?