A blank under 701510 has been shaped (curved, bent) but not optically worked — it lacks the ground and polished surfaces that give a finished lens its corrective power. Once the blank is ground to a prescription or polished to an optical surface, it classifies under the precision optics headings rather than here.

Mineral glass watch crystals fall under 7015. Sapphire crystals, however, are made from synthetic corundum rather than glass and classify under the headings for synthetic precious or semi-precious stones or worked precious stones, not under the glass chapter. The material composition determines the correct heading.