Materials science research on histrical changing of materials and techniques of anciet metal wire

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This research focuses to reveal the materials and the manufacture technology of an ancient gold wire excavated in an archaeological site in Japan, and also treats its history in Japan. Japan produces modern gold thread, which is made of the base film with thin gold surface. It is totally different from ancient gold wire. Ancient gold thread excavated in Japan was a strip-twisting wire type. This is the one of"filigrees", which is used injewelry to designate ornaments made from metal wires. Since the compositions of this gold wire were over 95 % gold and 4% silver, the material was soft enough to make it thin. The SEM observation tells us the details of this wire. Firstly, a gold foil, about 15μm in thickness, was made. Narrow strips, about 300μm in the width, were cut out from the foil with a kind of shears or scissors. Finely, a strip was twisted into a fine hollow tube with a round cross-section, which had a diameter of about 150μm. A single seam runs in a helix around the wire. The hollow wire shows deformation easily. Although it is an idea that it originally had silk threads as a core inside, the traces of organic materials were totally disappeared. The special gold earring made by layered gold foils was discovered. This technique was named "gold foil layering technique". It is very interesting thin gold foil was the first important stage of ancient gold wire excavated in Japan.