What 16th-century developments shifted diamond cutting to genuine faceting?

• A. The 16th-century developments of continuous rotary motion and the cast-iron polishing wheel shifted diamond cutting from superficial polishing to genuine faceting.
• B. The invention of the bruting machine and the motorized diamond saw.
• C. Advances in laser processing and rough mapping.
• D. The advent of mass production via automated flaking.

Answer: (A)

Diamond faceting relies on precise, repeatable motion and a stable, hard polishing surface. In the 16th century, cutters shifted from merely smoothing surfaces to creating flat facets by using continuous rotary motion, which allowed the diamond to be ground against a wheel in a controlled way around its circumference. Pairing that with a cast-iron polishing wheel provided the rigidity and durability needed to endure many precise, angular cuts. This combination enabled the formation of multiple flat facet planes with accurate angles, producing genuine faceting rather than just superficial polishing.

Earlier methods lacked that sustained, controlled rotation and a solid polishing medium, so surfaces remained mostly rounded or only lightly smoothed. The other options describe tools or technologies that played roles in later periods (or in other industries) and were not the driving force behind the 16th-century shift to faceting.