I make a bunch of small "paring knife" sized camp knives or patch knives out of old hand-saw blades and spike antlers. After I finish them, I make up a batch of STRONG tea - from that cheap instant stuff - just mix it in tap water. I then soak those knives in it for a few hours to a couple days. The longer they soak, the darker the antler gets - up to a point. It really blends in the cut and sanded parts with the rest of the horn. You get a good dirty-used-aged look.
I've used the potassium permangate stuff, also. It does a pretty good job. It has a purple-ish look as you are applying it, but dries to various shades of brown. When I use it, I usually put on two coats, let them dry, and then do the soaking in strong tea. It just helps balance out all the colors. And it's easier to put it on small areas - like touching up a knick on a handle. Be careful with the PP chemical. It will stain any organic material that it touches - like you skin, or clothes, or wood table tops! It can quickly lead to another of those "discussions", like when you are cooking up your "horn soup" on the kitchen stove!
Just some humble thoughts to share.
Mike Ameling