Researches on the Materials Science for the Ancient Bronze Mirrors focused on the Heat Treatment.

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We carried out researches into the heat treatment technique to ancient bronze mirrors for the aim at improvement of toughness, farther, corrosion of ancient bronze mirrors in clay. We obtained the following principal results.1. Toughness of the home made high tin bronze alloy was improved remarkably when, for example, water quenching from 720℃ of solution treatment and 20 minutes holding was performed.2. The rates of density reduction obtained from the measured and the calculated densities corresponded to the degree of corrosion of the mirrors.3. The shapes of appearances of pure copper lumps in the mirrors show various modes, i.e., depositions like layers, large or fine particles, or depositions like string or flash of lightning just burring the cracks in the mirrors.4. The oxide copper (Cu_2O) layers and particles were observed in the mirrors showing just the same shapes as those of pure copper depositions.5. Amorphous SiO_2 had formed in the outermost corroded layer.6. Cu_2O (cuprite) and Cu (OH)_2 had formed in the middle layer of corrosion, which comprise the first two internal layers adjacent to the layer.7. Cu-Sn-Pb-complex oxide had formed in the middle layer corrosion, the next internal layer. Small amounts of PbSO_4 and an Sn-organic compound were also detected. We observed that Cu_2S (chalcocite) forms like mold on the polished surface of the corroded layers, especially notable on layer IV, after being mechanically polished and left to stand for about one month. Cu_2S is presumed to be the resultant of sulfate reducing bacteria.8. Numerous pure copper lumps appeared in layers or particles and tended to form in the vicinity of the middle corrosion layer.9. The evidence from these analyses suggests that microorganisms could have been the cause of the corrosion found in ancient bronze mirrors excavated from clay.