In a wood matrix, inlays commonly use wood veneers, but other materials like shells,mother-of-pearlhorn or ivory may also be used. Pietre dure, or coloured stones inlaid in white or black marbles, and inlays of precious metals in a base metal matrix are other forms of inlay. Master craftsmen who make custom knives continue a tradition of ancient techniques of inlaying precious metals; additionally, many new techniques which use contemporary tools have also been developed and utilized as well by artisans.