Glass frit used as a coloring, opacifying, or decorating agent in the ceramic, enameling, or glass industry is specifically provided for under 320740. Frit intended for other uses — such as a raw material for glass fiber or flat glass production — may classify elsewhere. The intended industrial application and the product's formulation for decorative or coloring purposes are the key classification factors.

Vitrifiable enamels are glass-forming compositions designed to fuse onto a substrate during high-temperature firing, creating a glassy, chemically bonded surface layer. Paints and varnishes under headings 3208–3210 cure or dry at ambient or moderate temperatures through polymer film formation. The firing/fusion mechanism and the resulting glassy matrix distinguish vitrifiable enamels from conventional coatings.