The thickness of the bolsters will be determined, to an extent, by the thickness of the scales and how much they are to be tapered. The brasses, which includes nickel silver/German silver, are probably the easiest to work with. Bronze and aluminum might also work as well as other metals. Steel is more durable with stainless steel adding rust resistance. Mokume gane and pattern welded damascus, which is makume gane in steel, adds to the looks of the knife. They also add to the expence of making the knife. Some makers have even used non metalic material like horn or micarta for bolsters to good effect. I've even seen recon stone being used but I would put that on a knife that was a "looker" rather than a "user" as it can be a bit fragile. Pinning bolster can be done with the same material, at least for the metals, or with something that makes an interesting contrast. Another way would be to solder of braze them on. Epoxy could be use but a hard blow might break them off. Of course if the knife is something destined for a show case that's not a major issue; using the knife with a baton to split the pelvis of large game would be.
Doug Lester