all imported stag or antler from Pakistan or India is soaked in a mix of Potassium Permanganate to kill any parasites, disease, etc.
PP is a strong, caustic oxidizer and should be treated with respect. Oxidizers feed explosions or create burns.
The dark brown, dark red or even black surface color you see on imported stag is the result of soaking in PP. Stag antler is normally bleached out white, much like north American whitetail or moose antler.
PP is commonly used in water softeners and can be purchased in crystal form at most Sears stores or from a water softener company. You don't need much.
Mix up some (no good guidelines here - sorry. start with a few tablespoons in a quart of water) put in the antler and let it soak for a few minutes. Check it. At first it will be purple and then with more time, it will start turning red, brown and finally black when it has soaked too long. Leave it in over night and you end up with a dissolved pile goo in the bottom of your (plastic or glass) soak tub. Been there.
Wear heavy plastic glove. Any, ANY splashed on you will stain your skin and possibly burn you. Not right away but it builds up with an itch, then gets hot. You will not need to be told. It will get your attention. It will ruin clothes. It will throw off nasty, probably toxic odors.
With all of that baggage, it is still the most common way to die/stain antler.
Amber dying by Culpepper is a different, good process and tends to die deeply into bone or antler. Culpepper won't say how their process works as it is a proprietary secret.