To turn oak black,take some really rusty nails and other steel pieces and soak them in white distilled vinegar for a couple of days, then wipe on the wood. Gives oak a nice ebony look. Fuming white oak with amonia will also turn it a beautiful color(not black) its what the Stickley workshops used to color oak furniture. Fuming with amonia will even color varnished oak. I'll have to find my book on chemical staining for more examples.