Kautilya's Arthashastra 2.13.42

2.13.42

tāmrapādayuktaṃ rūpyaṃ rūpyapādayuktaṃ vā suvarṇaṃ saṃskṛtakam, tasmād rakṣet //

For setting jewels in gold, five parts of káñchana (pure gold) and ten parts of gold alloyed with four parts of copper or silver shall be the required quantity (mána). Here the pure gold shall be preserved from the impure gold.