Rasarnava 9.6

9.6

ṭaṅkaṇaṃ śataśo devi bhāvayet kiṃśukadravaiḥ
viḍo vahnimukhākhyo 'yaṃ lohānāṃ jāraṇe priye //

O Devī, one should process borax a hundred times with juices of the flame-of-the-forest.
This alchemical flux is named Vahnimukha ("Fire-Faced"), for the digestion of metals, O beloved.