Subheading 690912 covers ceramic articles — regardless of shape or end use — whose material hardness equals or exceeds 9 on the Mohs scale. This typically includes high-purity alumina (Al₂O₃) and silicon carbide ceramics used as wear-resistant components, cutting inserts, or precision substrates. The hardness must be verifiable by standard mineralogical testing; the article's commercial description alone is not sufficient for classification.

Heading 6909 covers laboratory and technical articles made of ceramic materials (fired clay, porcelain, alumina, etc.). Equivalent articles made of glass — beakers, flasks, tubing — fall under the chapter on glass and glassware. The material of construction is the primary dividing line; a borosilicate glass beaker and a porcelain crucible serving the same lab function classify in entirely different chapters.