Recently, the Emperor Qin Terracotta Warriors National Treasures and Cultural Relics Exhibition displayed bronze swords, copper spears, copper crossbows and other bronze weapons unearthed from the Mausoleum of the first Emperor in Chinese history alongside the tomb's world famous Terracotta Warriors.
Amazingly, the weapons shone without a hint of rust, appearing as new as the day they were buried over 2000 years ago. According to Peng Wen of the Emperor Qin Terra-cotta Museum, the secret lies in chemical chrome plating.
With electron probe micro-analysis and laser analysis, the China Research Institute of Nonferrous Metals and the Chinese Academy of Geological Sciences discovered that bronze swords unearthed from the mausoleum are coated with about 10 to 15 microns of chromium salt oxide.
The discovery indicates that during the sword-smithing process, ancient Qin workmen consciously added Chromate and Dichromate to the bronze weapons, producing a light grey or dark gray sheen. The workmen thus improved the corrosion and rust resistance of the weapons, while maintaining their luster and sharpness.
Chromate oxidization is an advanced technique and there are only two ways to achieve it: chemical chrome plating and chromium electroplating. The latter was development during the twentieth century; Germany and the U.S. both claimed patent rights to the process in 1937 and 1950, respectively.
Apparently, the ancient Chinese developed chemical chrome plating techniques more than 2000 years earlier, undoubtedly a miracle in the history of metallurgy.
(Chinanews.cn March 17, 2005)
