Qin-dynasty Bronze Sword

The secret to making bronze swords like this one with a sharp cutting edge and a long, slender shape lies in the percentages of copper and tin in the alloy. While a higher proportion of tin would make the swords harder and sharper, extreme hardness means vulnerability to fracture. It is the same case with copper, which could improve the ductility of the alloy while too much means softness. That’s why the bronzesmith in ancient China tended to use the alloy with a higher percentage of copper to the ridge of swords to maintain tensility, and that with more tin for the cutting edge to make it sharp. It is the state of Qin during the Warring States period (475 or 403-221 BC) that found the optimal proportions of tin and copper for swords combing stiffness and ductility. With the help of this recipe, the Qin state was able to cast the best swords, with an average length of over 90cm, among all the states during that period, which played an important role in its successful reunification of China.