शुल्बं तारं वा गर्भः पत्त्राणां संघात्येषु क्रियते ॥ कZ_०२.१४.३० ॥
śulbaṃ tāraṃ vā garbhaḥ pattrāṇāṃ saṃghāṭyeṣu kriyate
In leaf-laminated compactions, copper or wire is made the ‘core’ (garbha) inside (i.e., the interior is base metal while the exterior is leaf).
Placing a cheaper metal core (copper/wire) inside a laminated leaf structure so the outside looks precious while the inside is not.
Assaying must test interior composition (cut tests, drilling, density checks), not only surface appearance.