The Compendium of Kāśyapa 8.13.55

8.13.55

ṣaḍetāḥ samabhāgāḥ syuḥ saptamaṃ tāmrajaṃ rajaḥ
jalapiṣṭā bhavedetāḥ sūryataptāḥ punaḥ punaḥ

these should be six equal parts, and copper dust the seventh. / These should be ground with water and repeatedly heated in the sun;