A favorite trick used by builders of early styled long rifles is to apply linseed oil and then sprinkle bone black over it and then wipe off thoroughly. The bone black will embed itself in the wood fibers and leave a nice dark brown/black color. I have used it on recut checkering and it works great. Use an old toothbrush and paper towels to remove the surface oil. Bone black can be difficult to find but I believe Brownell's used to carry it. I have thought thoroughly pulverized artist charcoal sticks would work as well but have not tried it.
Oh, judicious use of bone black on restoring stocks is a good way to give them an aged patina and not appear so out of place on a vintage gun.
