Anandakanda 1.16.101

1.16.101

tailāvaśiṣṭaṃ vipacet tatpiṣṭvāyasapātrake /
nikṣipecca parīkṣārthaṃ kākapakṣaṃ vilepayet //

One should cook until the oil remains. Having ground it, one should place it in an iron vessel.
And for the sake of testing, one should smear a crow's feather