I have used the stain called Aquafortis on maple and walnut before. What it is is (degreased) steel wool dissolved in Nitric acid. You paint it on and let it dry completely. The acid dissolves the iron out of the steel wool and carries it down deep into the wood. After drying you go over it with a heat gun and watch the clors turn from red / green to brown to completely black. Don't overheat any area too much or it will scorch the wood but don't quit heating too early either or you will have an incomplete color change. After cooling you go over it with fresh (Degreased) steel wool and that will make the figure show up better. I degrease the steel wool by soaking it in Acetone, then letting it dry out.