Module:  The Power of Metal in
                     the Ancient Andean World

Theme:

The characteristics of the metallurgical technologies that arose and developed in the Andean region of South America during the prehistoric period reflect Andean cultural attitutdes about metal as a material. Andean peoples designed a range of alloys to exhibit certain highly valued physical, sensual properties, such as color. The processing of these alloys also ensured the mechanical integrity of objects made from them. Metal objects that were central to political and ritual spheres of Andean life communicated power through the materials of which they were made and the particular ways in which those materials were processed.

Module program:

During the course of the module participants will explore several subject matters. In morning sessions we will consider the salient technological features of Andean metallurgy, the underlying cultural principles that stamp the metallurgy and its products as typically Andean, and the physical metallurgy behind the processing of Andean alloys as the alloys were made into objects. We will entertain these subjects through an interplay of lecture and informal discussion.

Participants will spend afternoon sessions in the laboratory. The laboratory experience has two goals: (1) to demonstrate how a systematic materials-analytical study of Andean metal artifacts by metallography, electron microscopy, and other appropriate methods leads to the scientific characterization of Andean metallurgy; and (2) to have participants engage in the manufacture, processing, and property development of certain classes of Andean alloy.

Material culture component:

We will use a comparative method to identify and examine the underlying Andean cultural attitudes and precepts that strongly affected the ways in which indigenous metallurgies developed in the Andean region. The first comparison will consider the major differences between the metallurgies of the ancient Old World (western Asia, Europe) and New World (Andean S. America). This comparison will illustrate the social arenas that stimulated the development of metallurgy in each of these two parts of the world, the kinds of objects people primarily made from metal, and the properties they sought to develop in their alloys. Having established the sophistication of these two ancient metallurgies and the distinct differences in the social purpose of each, we will focus on characterizing Andean metallurgy. Using materials science studies of Andean artifacts reported in the literature, we will examine the metals and alloys that formed the backbone of the technology, the processing regimes used to manufacture stock metal for object fabrication, and the mechanisms used to produce metal objects that displayed culturally required colors. A second comparison will be drawn betweeen the principles that appear to have governed the specific ways in which Andean peoples thought about and handled metal as a material and the principles behind Andean cloth production. Cloth was the material good of greatest aesthetic, political, and religious value in the ancient Andes. This comparison, which is internal to Andean society, seeks to discover any regularities between the ways in which people handled metal and the ways in which they managed fibres. Both the external comparison, with the Old World, and the internal comparison between two important Andean materials technologies, will help locate the cultural content of Andean materials development. We should begin to appreciate how the selective use of certain materials and the processing of those materials imbued metal objects with power in Andean society.

Materials science/engineering and laboratory component:

Since most Andean metal objects were made from hammered metal sheet, the physical metallurgy component of the module will concentrate on how metals are shaped by plastic deformation. We will consider basic crystalline structures, especially of fcc metals, grain rotation and orientation during deformation, the role of dislocations in slip, work hardening, annealing, and recrystallization. Participants will become familiar with the metallic microstructures that provide evidence for the processing sequence an artifact has experienced during its manufacture. We will also study the phase diagram of the copper-silver system -- the primary Andean alloy considered in the module -- to familiarize participants with phase diagrams in general and with eutectic systems in particular. They will learn how the surface color of objects made by the plastic deformation of this and similar alloys is altered during processing through mechanisms of depletion and enrichment of near-surface alloy elements.

The laboratory: Participants will rotate through three laboratory units. Unit 1: Basic microstructural analysis. Using metallurgical microscopes, participants will examine sections prepared from (a) non-ferrous metals/alloys whose microstructures exhibit the characteristic features of plastically deformed metal; and (b) Andean artifacts made from the alloys presented in the module. These artifacts underwent surface enrichment and color alteration during their elaboration, and evidence of these procedures are present in their microstructures. Unit 2: Basic extractive metallurgy. This unit gives participants an opportunity to direct smelt copper ores with charcoal, producing copper metal. The unit will be carried out in the DMSE foundry. Unit 3: Plastic deformation and surface depletion of copper-silver alloys. Participants will sand cast copper-silver alloy ingots. They will hammer, anneal, and pickle the material as they fashion it into sheet. They will observe the change in suface color of the metal, from pink to silver, during processing. The unit will be carried out in the DMSE forge.