शुल्बं तारं वा गर्भः पत्त्राणां संघात्येषु क्रियते ॥ कZ_०२.१४.३० ॥
śulbaṃ tāraṃ vā garbhaḥ pattrāṇāṃ saṃghāṭyeṣu kriyate
संघात्येषु पत्त्राणां गर्भः शुल्बं तारं वा क्रियते।
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.