Rasendracudamani 14.148

14.148

nāgaḥ śuddho bhavedevaṃ mūrcchāsphoṭādi nācaret /
{bhrāṣṭrayantra}
tiryagākāracullyāṃ tu tiryagvaktraṃ ghaṭaṃ kṣipet /
taṃ ca vaktraṃ vinā sarvaṃ gopayedyatnato mṛdā /
bhrāṣṭrayantrābhidhaṃ caitannāgamāraṇam uttamam //

Thus lead becomes purified; it will not cause fainting, blisters, and the like. / [Bhrāṣṭra apparatus] / One should place an inclined-mouthed jar on an inclined furnace, / and, except for that mouth, cover everything with care using clay: / this is named the bhrāṣṭra apparatus, excellent for the incineration of lead.