I'm very particular with the quality of handle materials, and I never use artificial materials. Only the absolute best of natural materials will ever meet with my blades.
Apart from the odd knife with a bolster of horn , tusk or hardwood bolsters are filed out of brass or massive Sterling Silver.
The examples shown display (from left to right) the following combinations:
1. Sterling Silver/Walrus Tusk/Caucasian Walnut
2. Brass/African Buffalo Horn/Masur-birch
3. Sterling Silver/ Narwhale Tusk/Desert Ironwood
The handle materials proper fall in five major catagories:
Tusk (which are all legal ivory): Walrus (Greenland)
Hardwoods from the Northern Hemisphere: Curly Maple (North America)
Bruyere (Mediterranean Region)
Caucasian Walnut (Asia Minor)
Olive (Mediterranean Region)
Elm Root (Denmark)
Tropical hardwoods: Amboina (Indonesia)
Snakewood (Viet Nam)
Rio Palisander (Brazil)
Desert Ironwood (Mexico)
Horn: Buffalo horn (Africa & India)
Saigak Antelope (Uzbekistan)
Ram's horn (North America)
Musk Ox horn (Greenland)
Antler: Elk (North America)
Red Deer (Europe)
Of course there is almost no end to the combinations of all these.