An archaeometallurgical study of Mixtec silver gold alloy foils from Tomb No. 7, Monte Alban, Oaxaca, Mexico

Abstract

This work evaluates four groups of silver gold alloy foil samples from Tomb No. 7 from Monte Alban, Oaxaca. These were classified as received according to coloration as LG1, LG2, LG3, and LG4. These samples were called silver gold alloy foils because of their main elemental composition. These were analyzed (without alterations) via optical microscopy, scanning electron microscopy (SEM), and energy dispersive spectroscopy (EDS). It was necessary to prepare them by focused ion beam (FIB) cross section to know their real microstructure and finally to test their indentation hardness (HIT) and indentation modulus (EIT) to measure mechanical properties. The experimental results revealed that silver gold alloys were cold-worked and annealed using a mixed technique of hammering with intermediate annealing for grain-size refinement. These were modified in their mechanical properties. The LG2 sample was the thinnest (27 μm) and hardest foil (HIT ¼ 1781.7 MPa). It has the highest Au content (56.9 wt%) and the lowest Cu content (1.5 wt%) unlike LG4, which was the softest foil (HIT ¼ 325.1 MPa). This sample showed non-recrystallized grains: This was the major superficial damage and led to a deficient work metal.