Thanks for the help everyone
I've done this to. It involves soaking a batch of rusted cut nails, Stamped iron made from the early 1800's to about 1875, in cider vinegar. After a few weeks you would brush this ferrous (Iron) solution onto the wood. It would soak more into the end grain, the dark stripes, and increase the contrast between the stripes. The wood was dried including using flames,then smoothed and an oil finish was applied. It is dramatic, distinctive and unsuited to cues as way too much water is involved and it is hard to control.Some of the3 classic gun makers...those guys that make those beautiful Flint Lock Muzzle Loaders...us a chamical called Aquapherous (sp). It is a form of watered down acid that reacts slightly differently to the grains of the curly and birdseye maple. In the curly maple, the curl comes from the different desities in the grain. The acid (or stains for that matter) absorb more in the more opened grain. I believe they apply a little heat to make a better contrast between the two grains too. After they have reached the appearance they desire, they need to neutralize the acid with something else...maybe baking soda.
Some of those guns looks great and this might be a great process for cues as well I think. Just a thought.
L8R...Ken