Multilayered artifacts in the pre-Columbian metallurgy from the North of Peru

Abstract

Three types of alloys were recognized when analyzing pre-Columbian artifacts from the North of Peru: gold, silver, and copper alloys; gilded copper and silver; silvered copper; tumbaga, i.e., copper or silver enriched on gold at the surface by depletion gilding. In this paper, a method is described to differentiate gold alloys from gilded copper and from copper-gold tumbaga, and silver alloys from silvered copper and copper-silver tumbaga. This method is based on the use of energy-dispersive X-ray fluorescence, i.e., on a sophisticated analysis of XRF-spectra carrying out an accurate determination of Cu(K (alpha) /K (beta) ), Ag(K (alpha) /K (beta) ), Au(L (alpha) /L (beta) ), and Au-L (alpha) /Cu-K (alpha) or Ag-K (alpha) /Cu-K (alpha) ratios. That implies a dedicated software for the quantitative determination of the area of X-ray peaks. This method was first checked by a relevant number of standard samples and then it was applied to pre-Columbian alloys from the North of Peru

Gold, gildings, and tumbaga from the Moche tomb of the Lady of Cao: An EDXRF test for the internal ratio method

“…The method of using the altered internal ratio of K or L X‐rays of gold, silver and copper to differentiate gold from gilded copper, gilded silver, and tumbaga gives good results, as demonstrated by this paper and also by previous works . However, not in all cases, there is a clear answer; in a few cases, particularly of artifacts from the tombs of Sipán, it was not possible to clearly differentiate a poor gold alloy from a tumbaga.…”

“…Multilayered metal structures can be correctly interpreted, and the various layers thickness determined, by using energy‐dispersive X‐ray fluorescence (EDXRF) analysis and dedicating a deep quantitative study to the areas of X‐ray peaks.…”

“…The gilding composition (or equivalent gilding composition in the case of tumbaga) was determined in the usual manner, whereas the gilding thickness was determined from the ratios Au (Lα/Lß), Cu (Kα/Kß), Au‐Lα/Cu‐Kα, Ag (Kα/Kß), and Au‐Lα/Ag‐Kα. As described in previous papers, these ratios are altered with respect to the same ratios for thick metals, and the difference depends on the gilding thickness and composition. The gilding composition was determined in the hypothesis that no copper is present in the gildings or in the tumbaga equivalent thickness.…”

Use of Monte Carlo Simulation as a Tool for the Nondestructive Energy Dispersive X-ray Fluorescence (ED-XRF) Spectroscopy Analysis of Archaeological Copper-Based Artifacts from the Chalcolithic Site of Perdigões, Southern Portugal

“…2b). [28][29] For this purpose, all the measured spectra were modeled as two-layered structures formed by: (a) the inner bulk layer; and (b) the outer superficial layer composed by the green oxidized corrosion patina and the brownish carbonate soil-derived encrustation.…”

The structure of two‐layered objects reconstructed using EDXRF‐analysis and internal X‐ray ratios

“…The theoretical background of these methods has been discussed in detail elsewhere. [7][8][9][10][11][12] However, a few basic equations will be given in the succeeding paragraphs.…”