I am the acquaintance Dave mentioned. I use bone blackening to bring out grain flow I can see in open pored, bland colored wood. I mix the blackening in a pore filler and then work it into the stock just as you would use a normal pore filler. It looks like heck when first added as the whole stock looks black when first applied. Once applied, you knock it back like you normally would with any pore filler. IMO it is a good way to make an open pored, bland colored stock look better. Below is a rifle stock I finished using the method. Prior to the blackening there was no grain contrast in the finish.
