Sword production in China is attested from the Bronze Age Shang Dynasty. The technology for bronze swords reached its high point during the Warring States period and Qin Dynasty. Amongst the Warring States period swords, some unique technologies were used, such as casting high tin edges over softer, lower tin cores, or the application of diamond shaped patterns on the blade (see sword of Goujian). Also unique for Chinese bronzes is the consistent use of high tin bronze (17–21% tin) which is very hard and breaks if stressed too far, whereas other cultures preferred lower tin bronze (usually 10%), which bends if stressed too far. Although iron swords were made alongside bronze, it was not until the early Han period that iron completely replaced bronze.