अप्सु निष्ठ्यूतास्तैलवद्विसर्पिणः षङ्कमलग्राहिणश्च ताम्ररूप्ययोः शतादुपरि वेद्धारः ॥ कZ_०२.१२.०३ ॥
apsu niṣṭhyūtās tailavad visarpiṇaḥ ṣaṅkamalagrāhiṇaś ca tāmrarūpyayoḥ śatād upari veddhāraḥ
When spat into water, if it spreads like oil and takes on a conch- or lotus-like pattern, it is a piercing/assaying substance yielding copper or silver in excess of a hundred (units).
Because it is low-cost, repeatable, and deployable in remote sites—supporting quick screening before committing state labour, guards, and smelting capacity.