Sutcliffe I've only done this once. I used a combination of tea and coffee to dye a piece of Elk antler. It resulted in a beautiful golden brown color. I left the antler in the solution for a couple of days. I noticed 2 side effects though. After I thought it was dry, I started to clean out the center for my hidden tang. I found the inner spongy core, which is usually a pain to drill out, became extremely brittle. It only took me about 5 minutes to easily make the slot for the tang. This is one side effect. I then proceeded to fit the guard and drill a hole in the handle for the pin. About a week or two later, after the knife was treated, I was assembling the handle and was having difficulty tapping the handle pin in. I gave it a couple of firm whacks and turned the handle over to see it the pin was all the way through and discovered the second side effect. The soaking had caused the antler to shrink. I didn't notice this and consequently cracked the opposite side of the handle when I was pounding the pin home. I don't know if it was just bad luck on my part but you may want to let your antler sit for a couple of weeks before you drill any holes.
Hugh
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King of all that rhymes with Orange!