After this stone is rubbed with castor oil, the gold is rubbed lightly across its face to leave a gold trace. The color of the trace is then compared to that of various bars, whose purity is already known, to determine the purity of the gold being tested.
使用前先用蓖麻油擦一下，再把待價而估的金子在石頭表面輕輕磨下一道金痕，然後拿起試金棒逐支比對。顏色與那支一樣，成色就是多少。