Decorative metal threads have been woven into textiles since ancient times to portray wealth and sociocultural importance. Often made of gold, silver, or alloys, the technique of manufacturing metal threads varied with resources, culture, and time. Unfortunately, these fabrication methods remain elusive, as little is described in written historical sources, and studies have been limited by number of threads, instrument sensitivity, or sample preparation method.1 There is considerable interest in identifying the metals used in these precious threads, as the composition of the metal and gold/silver ratios are possible identifiers of provenance.2 A highly sensitive analytical method was developed to characterize the chemical composition of ancient metal threads using scanning electron microscopy with energy dispersive X-ray spectroscopy (SEM-EDX) and correlated micro X-ray fluorescence (micro-XRF) mapping. These complementary techniques provide a quantitative two-dimensional map the elemental composition with high spatial resolution, which contains valuable information about the thickness of the strips/wires, metal coating, chemical heterogeneities, and identification of surface coatings and corrosion products. The surface and cross sections of threads ranging from 12th century Japanese gilt-paper threads to 18th century French solid metal strips, were analyzed using the developed method to determine what production techniques were used, and as a basis for establishing a relationship between gold/silver ratios and trace elements patterns and the provenance of the threads. Most threads contained multiple layers, frequently gold, silver, copper, or zinc bulk layers were detected, and both gilt and drawn-and-pulled strips were observed. This unique application of spectroscopic mapping is indispensable for investigating the origin and fabrication of ancient metal threads, providing insight into the cultural and historical significance of these textiles and the development of metallurgy and gilding technology.

Imaging and analysis of ancient decorative metal threads using scanning electron microscope-based X-ray spectroscopies

2019 Fall National Meeting

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