Mediaeval metal threads and their identification using micro-XRF scanning, confocal XRF, and X-ray micro-radiography

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Year of publication 2019
Type Article in Periodical
MU Faculty or unit

Faculty of Arts

Keywords X-ray fluorescenceX-ray radiographyMetal threadMediaeval textilesGilding
Description Fabrics with metal threads were discovered in mediaeval well during excavations in the Mecova 2 Street in Brno. These are thin braids woven of metal threads using a small loom and sewed together into a broader strip. The textile materials are in a relatively good state, because the environment of the well preserved organic materials (fabrics, leather, wood). Furthermore, the positive effect of metal corrosion on the preservation of organic parts of the fabric occurred here. If metal threads are found in graves or dwelling backfills, only spiral-shaped metal fragments with microscopic relics of organic fibers are preserved. Based on microphotographs, we assume that metal threads were made by cutting or scissoring thin strips of metal sheets. The strips were spirally wound on a textile thread. The excavated fabric was deposited in a museum collection storage room for 20 years unnoticed, because its surface was covered with a layer of sediment and corrosion products. During the systematic research of mediaeval fabrics from Brno, it was found out that relics of gold are present in the ends of some of the threads. The fabrics were examined by non-destructive analytical methods. Metal threads covered with sediment and corrosion products were studied using X-ray fluorescence and radiography methods. The concentrations of elements in the individual layers show that the centre of the metal thread is formed by a silver strip. A thin layer of gold was laid on the silver strip. Silver was alloyed with copper, which corrosion products covered the whole metal strip and solidified the layer of sediments in the surface. XRF elemental mapping was employed to find out whether the metal threads pass through the whole braid. The results show that the braids are composed of silver threads with gold deposited on their rims and some central parts only.
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