Kautilya's Arthashastra 2.14.41

2.14.41

maṇayo rūpyaṃ suvarṇaṃ vā ghanasuṣirāṇāṃ piṅkaḥ //

Spurious stones and counterfeit gold and silver may be substituted for real ones in compact and hollow pieces (ghanasushira). They are detected by hammering the pieces when red hot---so much for confounding (pinka).