Structural and Mophological Studies of Precolombine Au-Based Craftsmanships

We report crystallographic and morphological analysis of pre-Columbian craftsmanship for evaluation and restoration after 500 years of production by native artisan. Gold pieces of the pre-Columbian culture from the \textit{andine} plateau were studied. Carefully Rietveld refinement of the X-ray diffraction patterns showed the characteristic Au structural phase, with incipient additional peaks, which correspond to non reactive Ni, Cr and Pt elements, to conform a microgranular composite. EDX spectrum reveals the presence of those elements and the semi quantitative analysis supplies values of 88{\%} Au, 6{\%} Ni, 4.5{\%} Cr and 1.5 Pt. SEM show three well recognized types of grain: one majority obscure topology of 8 -- 10 $\mu $m grain size; second with slightly more brightness of grains, 3 $\mu $m size; and a third kind of grains with mean size smaller than 3 $\mu $m. These results were corroborated by using AFM studies. We interpret the first grain regime as corresponding to Au; second to Ni and Cr; and third to Pt. Similar mixture was prepared by utilizing Aldrich 99.99{\%} precursors in order to perform the restoration of pre-Columbian pieces. The X-ray analysis of mixture showed the same behavior of initial studies of pieces.