Anandakanda 2.5.51

2.5.51

dinaikaṃ dhārayedgharme dravaiḥ pūryaṃ punaḥ punaḥ /
arjunaiḥ sāranālairvā trividhaṃ mārayedayaḥ //

One should keep it in the sun for one day, filling it repeatedly with the juices, / with arjuna or with fermented gruel; thus one kills the three types of iron.