The author-scholar, Ho Wei, precisely described the process of making cupronickel in about 1095 AD. The "paktong" alloy was described as being made by adding small pills of naturally occurring "yunnan" ore to a bath of molten copper. When a crust of slag formed, saltpeter was added, the alloy was stirred and the ingot was immediately cast. Zinc is mentioned as an ingredient but there are no details about when it was added. The ore used is noted as solely available from Yunnan, according to the story: