A pre-Columbian galvanic technique able to explain the gilding of copper in northern Peru

Around 150 BCE and 700 CE, pre-Columbian goldsmiths in the Peruvian northern coastline developed a method for gilding copper. The characteristics of the resulting pieces are substantially different from those obtained by hammering, embossing, and casting. We discuss two electrochemical gilding methods that were possibly developed by pre-Columbian goldsmiths. The first method consists of electrochemical replacement where copper is immersed in a solution containing dissolved gold. The second method utilizes the same solution but includes pyrite to form a galvanic cell with copper as the cathode and pyrite as the anode. Characterizations via X-ray fluorescence (XRF) and Scanning electron microscopy with energy dispersion spectroscopy (SEM-EDX) allowed a comparison of the results of the two methods with archaeological samples. The electrochemical replacement method does not reach thicknesses observed in archeological samples and delivers irregular gilding due to the formation of anodic spots on copper. Meanwhile, including pyrite as an anode in the electrochemical cell leads to a more homogeneous deposition of gold with layer thicknesses similar to those found in archaeological samples. This work contributes to understanding pre-Columbian techniques lost before the Inca Empire.