Anandakanda 2.6.20

2.6.20

drutadrāvaṃ mahābhāraṃ chede kṛṣṇaṃ samujjvalam /
pūtigandhaṃ bahiḥ kṛṣṇaṃ śuddhaṃ sīsamato'nyathā //

Lead that melts quickly, is very heavy, black and brilliant when cut,
foul-smelling, and black on the outside, is pure; otherwise it is impure.