कालायसस्यार्धभागाभ्यक्तं कृष्णं भवति ॥ कZ_०२.१३.५५ ॥
kālāyasasyārdhabhāgābhyaktaṃ kṛṣṇaṃ bhavati
Jika dilapisi/diolah dengan setengah bagian besi hitam (kālāyasa), hasilnya menjadi hitam.
Surface treatments can disguise base metals; state knowledge of such methods supports enforcement against fraud in bullion, ornaments, and coin-like pieces.