《明史·志·卷五十七》
随后工部上奏说： 山西交城出产云子铁，旧时进贡十万斤，修缮打造兵器，别处没有。 
既而工部言： 山西交城产云子铁，旧贡十万斤，缮治兵器，他处无有。 
After that Ministry of Works reported that: there was cloud son iron produced in Jiaocheng of Shanxi, 100,000 catties were presented as tribute in old times, and it was used for repairing and making weapons; there was none elsewhere. 