The heading explicitly covers three substrate types: base metals (such as copper or nickel), silver, and gold. The substrate identity can affect valuation and, in some cases, classification at the HTS 10-digit level, so importers should clearly document the substrate composition and the thickness of the platinum-group-metal layer on the commercial invoice.

The boundary is 'not further worked than semimanufactured.' Once the plated material is cut, formed, stamped, or assembled into a recognizable article — such as an electrical contact, a crucible, or a piece of jewelry — it is classified by its finished form rather than as a plated precious-metal intermediate. Importers of partially fabricated components should review the degree of working carefully with a licensed customs broker.