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板凳
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发表于 2019-1-27 20:06:45
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Gold-filled cases were made by sandwiching together 2 bars of gold (typically about 1/2" thick) on either side of a bar of base-metal, usually brass or brass-alloy (typically 3/4" thick). The 3 bars were soldered together under high pressure and high temperature in specially constructed ovens. The composite 3-layer bar was then rolled through high-pressure rolling mills until the desired thickness was reached. The gold layers could consist of 10-karat, 14-karat or 18-karat gold. While this process produced a thicker layer of gold than electro-plating, the gold content was still no more than 5-10% of the total case weight. As such, gold-filled watches do not have any significant gold value.------包金的做法 |
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