Take a look at the process and techniques used. Millefiori, Mokume Gane, PMC and more.
Once a clay piece is finished and baked, it goes through a sanding and buffing process anywhwere from six to twelve steps, from 400 grit up to 12,000 grit. (yes, 12,000, not a typo!) PMC sterling is fired in a kiln, then tumbled, sanded, polished, etc.