Which term best describes the surface's appearance under reflected light?

Which term best describes the surface's appearance under reflected light?

• A. Luminescence
• B. Dispersion
• C. Brightness
• D. Luster

Answer: (D)

Luster describes how the surface reflects light—the shiny, glassy, silky, or dull finish you see when light hits the gem. It’s the standard term for describing surface appearance under reflected light, capturing the quality of the surface reflection itself. Luminescence would be light the gem emits, not just reflects. Dispersion is about splitting white light into colors (fire) within or from the stone, not the surface shine. Brightness refers more to how much light is returned, but luster is the descriptive term used for the surface’s reflective quality.

Luster describes how the surface reflects light—the shiny, glassy, silky, or dull finish you see when light hits the gem. It’s the standard term for describing surface appearance under reflected light, capturing the quality of the surface reflection itself. Luminescence would be light the gem emits, not just reflects. Dispersion is about splitting white light into colors (fire) within or from the stone, not the surface shine. Brightness refers more to how much light is returned, but luster is the descriptive term used for the surface’s reflective quality.