Kautilya's Arthashastra 14.2.8

14.2.8

śvetabastamūtre śvetasarṣapāḥ saptarātroṣitāstakra(?).marka..kṣīralavaṇaṃ dhānyaṃ ca pakṣasthito yogaḥ śvetīkaraṇam //

The pastry made from white mustard seeds kept for seven nights in the urine of a white goat mixed with butter-milk, the milk of arka plant, salt, and grains (dhánya), causes, when applied for a fortnight, white colour.