There has been debates about different joints Ivory, stainless etc etc, as far as i know nobody can really call out what type of joint they are playing with if the joint is covered.
I feel what it really comes down to is the hardness of the tip, the taper and type of wood and what MM the thickness of the shaft is. I myself have a solid Ivory joint with a pure silver ring wrapped around it. and i could not tell the difference with my stainless steel joint. but i can with the Shaft.