Rasarnava 7.21

7.21

kṣārāmlagojalairdhmātaṃ śudhyate ca śilājatu
athavā goghṛtenāpi triphaladvyārdrakadravaiḥ
lohapātre vinikṣipya śodhayettattu yatnataḥ //

Blown with alkalis, acids, and cow's urine, bitumen is purified;
or indeed, placing it in an iron vessel with cow's ghee
and the juices of triphalā and fresh ginger, one should purify it with effort.