Surface Manipulation in Cu- and Ag-Based Pre-Columbian Artifacts.

Area of Science:

• Archaeometallurgy
• Materials Science
• Moche Civilization Studies

Background:

• The Moche civilization (ca. 450 AD) in Peru produced exceptional metal artifacts.
• The Lady of Cao's tomb revealed a high-status woman with rich grave goods, including intricate metalwork.
• Notable artifacts include gilded objects and bimetallic nose ornaments.

Purpose of the Study:

• To investigate the sophisticated metalworking techniques employed by Moche artisans.
• To understand the material science behind the creation of Moche gold and silver artifacts.
• To analyze the methods used to create layered and bimetallic surfaces.

Main Methods:

• Analysis of copper (Cu)-, silver (Ag)-, and gold (Au)-based alloys in Moche artifacts.
• Microstructural examination of thin surface layers (3-5 μm) on artifacts.
• Identification of subtractive surface treatment techniques, including selective copper depletion.
• Evidence of epitaxially grown silver wires supporting surface manipulation hypotheses.

Main Results:

• Moche metalworkers expertly produced and shaped Cu- and Ag-based alloys.
• They created thin, uniform gold- and silver-enriched surface layers using etching agents.
• Selective depletion of copper from alloys and removal of elements from ternary alloys were employed.
• The formation of micrometric silver wires suggests a pioneering nanoscale surface treatment.

Conclusions:

• Moche artisans possessed a sophisticated, empirical understanding of alloy production and surface manipulation.
• They utilized subtractive techniques to achieve specific monometallic or bimetallic appearances.
• This mastery of micro- and nanoscale material modification enabled the creation of unique artistic and symbolic artifacts.