कालायसस्यार्धभागाभ्यक्तं कृष्णं भवति ॥ कZ_०२.१३.५५ ॥
kālāyasasyārdhabhāgābhyaktaṃ kṛṣṇaṃ bhavati
काले लोहे (कालायस) के आधे भाग से लेप/उपचार करने पर वह काला हो जाता है।
Surface treatments can disguise base metals; state knowledge of such methods supports enforcement against fraud in bullion, ornaments, and coin-like pieces.