Kautilya's Arthashastra 2.14.52

2.14.52

virūpāṇāṃ vā tāpanam udakapeṣaṇaṃ ca bahuśaḥ kuryāt //

In all those pieces which are hammered, cut, scratched, or rubbed the loss can be inferred by comparing them with intact pieces of similar description. In amalgamated pieces (avalepya) which are cut off, the loss can be ascertained by cutting off an equal portion of a similar piece. Those pieces the appearance of which has changed shall be often heated and drenched in water.