Anandakanda 2.1.248

2.1.248

athavā śukapicchābhamantaḥ kāñcanabindubhiḥ /
aṅkitaṃ gharṣayettuttham āyase cāmlasaṃyute //

Alternatively, it has the lustre of a parrot's tail-feather, marked inside with golden specks;
one should rub this vitriol onto iron together with sour liquid;