Anandakanda 2.2.16

2.2.16

piṣṭvā limpetsvarṇapatraṃ bhasmacchannaṃ tu karpare /
yāvaddravaṃ puṭaṃ tāvatkuryāttena viśudhyati //

one should smear gold leaves [with it] and, covered with ash in an earthen vessel,
subject it to fire in a pit until it is liquid; through this, it is thoroughly purified.