I was goofing around with ebonizing also a while back. Did not try ink though, sounds interesting.
I had the most success on light color wood, doing a three step process. First was wetting the wood out with a tannic solution, followed by a iron/vinegar solution. After that dried, rubbed it down hard with a rag and then used Transtint black. Turned out jet black on Maple and Englemann Spruce, which was surprising.