Indagini sul Corredo Funerario dell'enigmatica Signora di Cao: Parte Prima, Decorazioni Nasali

During excavations in the archaeological complex El Brujo (The Wizard), in the North-East side of Huaca Cao Viejo, 70 km north of Trujillo, in Peru, in the year 2005, it was made one of the most important discovery concerning the Moche culture: a tomb containing the mummy bundle of a high hierarchy woman, which is referred to as “Lady of Cao” and dates about 300 A.D. The high hierarchic level of this woman was deduced from the objects she took with her in the tomb. The coffin of the Lady contained more than hundred objects, mainly on gold and silver. In this paper are reported the results of Energy Dispersive X-Ray Fluorescence (EDXRF)-analysis on 34 nose decorations on gold and silver from the tomb of the Lady of Cao. The purpose of this investigation, that followed a similar one carried out previously in the Museum "Tumbas Reales de Sipan", was to investigate the evolution of Moche metallurgy. EDXRF-analysis is a non-destructive and non-invasive technique which in the case of metals analyzes micrometric surface layers. Therefore it can give wrong results when the sample composition is altered because of surface processes. A complementary echnique was therefore developed, of bulk analysis, using X-ray transmission of monoenergetic X-rays. It uses the same equipment employed for EDXRF-analysis; the X-ray beam from the X-ray tube is monochromatized by means of a tin secondary target, which K-lines bracket the silver-K discontinuity. This technique is able to determine, (by measuring the attenuation of tin-K rays), thickness and/or composition of gold and silver alloys having a thickness of less than about 120 μm for gold and about 0.7 mm for silver. The method as tested with Au-Ag-Cu alloys of known composition and thickness, and then applied to gold and silver artifacts from the tomb of the Lady of Cao. X-ray transmission measurements on gold and silver sheets approximately confirm the results of EDXRF-analysis.

In questo articolo sono riportati I risultati delle analisi effettuate con XRF su 33 decorazioni nasali della Tomba della Signora di Cao del Peru.Dai risultati ottenuti sulle decorazioni nasali della signora di Cao si possono trarre le seguenti conclusioni: -le parti in oro hanno una composizione simile in tutte le 33 decorazioni, con le seguenti composizioni medie : Au=(78.0±2.5) % ; Ag=(17.5±3) % ; Cu=(4.5±1.0)% ; -le parti in argento hanno una composizione del tutto erratica, con i seguenti valori estremi : Au=(40-100)% ; Ag=(0-40)% ; Cu= 0-35)% ; -la presenza di così rilevanti percentuali di oro nelle parti in argento è del tutto inusuale nell’oreficeria antica e moderna ; -le misure in trasmissione confermano in linea di massima le analisi EDXRF.