Inlay is a decorative technique of inserting pieces of contrasting, often colored materials into depressions in a base object to form patterns or pictures that normally are flush with the matrix. In a wood matrix, inlays commonly use wood veneers, but other materials like shells, mother-of-pearl, horn or ivory may also be used. Colored 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.