http://press.princeton.edu/titles/10571.htmlAccording to this:
- The goods brought in by the Japanese [during the Ming dynasty] consisted, among other things, of swords in great number and quantities of copper ore and sulfur, the last used in gunpowder.
https://books.google.com/books?id=6AeGAAAAIAAJ&q=%22the+goods+brought+in+by+the+Japanese%22&dq=%22the+goods+brought+in+by+the+Japanese%22&hl=en&sa=X&ved=0ahUKEwigx9f5n57gAhVCMn0KHYfLDGoQ6AEIKjAA
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