Anandakanda 2.1.18

2.1.18

lohapātreṇa ruddhvātha pṛṣṭhe sthāpya ca kharparam /
sāgnim utpalakaiḥ pūrṇameva drāvya samuddharet //

Having covered it with an iron vessel, and having placed an earthen saucer with fire / full of dried cow-dung cakes upon it, melting it in this way, one should extract it.