Hi all!
I all depends on the materials and the effects you want to get, especially if you are talking about handles.
For wood handle material you may try a propane torch/steel wool treatment or a coffee/mud mixture. Both are difficult because the heat of the propane torch may shrink the wood and the water in the coffee/mud may swell it.
For antler it is a lot easier as you can work with potassium hypermanganese (i hope the spelling is ok, i am german) which will give the white areas a deep brown colour. It is a dark purple coloured grainy powder you can get in drugstores, which is used for mouth disinfection. Just make a 5 % solution and dip the handle in. The solution has a purple colour, but don't worry, the antlers get the same dark brown colour as your skin when you touch it. Let soak for 5 minutes and dry.
For leather i take a thick brown leather stain, which i apply, let dry and remove with alcohol. Gives a very mottled surface.
In general, if i want the antique look, i prefer using antique materials like very old antler or cracked ivory. Silver fittings blackened with egg white or ferric cloride to go with.
Have fun!
Achim