History of Chemistry in Ancient and Medieval India, Incorporating the History of Hindu Chemistry by Acharya Prafulla Chandra Ray c18.6

c18.6

5. One desirous of purifying copper is to make it thin and it is to be steeped in acid (*amla*, *skyur po’i. nan. du.*) for seven days, and likewise in whey (*dar. ba’i. chur khu. la*) and it becomes glossy (*legs. par. bkra. bar. bya’o*). Then the copper with an equal portion of sulphur is to be put in an earthen pot, so that (when it is placed in fire) no smoke can come out. And then it becomes white just like silver.