कालायसस्यार्धभागाभ्यक्तं कृष्णं भवति ॥ कZ_०२.१३.५५ ॥
kālāyasasyārdhabhāgābhyaktaṃ kṛṣṇaṃ bhavati
При покрытии/обработке половиной части чёрного железа (kālāyasa) оно становится чёрным.
Surface treatments can disguise base metals; state knowledge of such methods supports enforcement against fraud in bullion, ornaments, and coin-like pieces.