Kautilya's Arthashastra 2.14.39

2.14.39

abhrapaṭalam aṣṭakena dviguṇavāstuke vā rūpe badhyate //

In some pieces, mica may be firmly fixed inside by wax and covered over with a double leaf (of gold or silver). When such a piece with mica or glass inside is suspended in water (udake) one of its sides dips more than the other; or when pierced by a pin, the pin goes very easily in the layers of mica in the interior (patalántareshu).