Data from laboratory studies of chemical composition and fabrication techniques of some 400 prehispanic metal artifacts from the Museo Regional de Guadalajara collections were used to identify two primary artifact groups. One consists of objects made from copper, the other of subtypes of the same artifact types made from copper-arsenic, copper-tin, and other alloys. The studies showed that these artifact subtype/materials associations were often technically imperative. A two-phase chronology for the West Mexican metallurgical technology was constructed by bringing these data to bear on datable artifacts. From approximately A.C. 800 to between A.C. 1200 and 1300, copper was used to manufacture bells, tweezers, and other objects by lost-wax casting, cold work, and other techniques. Between A.C. 1200 and 1300 to A.C. 1520 copper was used as before but morphologically distinct subtypes of these artifact classes also appeared, whose designs required the alloys. The work reported here is the first to identify associations between designs and materials that characterize particular artifact classes and to use them to construct a chronology. The presence of the artifact types described here can be used to date, in approximate terms, otherwise undatable material and employed as an independent source of temporal information for archaeological material for which approximate dates may already exist.