Which property governs light performance and thus the stone's brilliance and fire?

• A. Carat weight
• B. Color
• C. Clarity
• D. Cut

Answer: (D)

Light performance in a gemstone is determined by its cut, because how the facets are proportioned, aligned, and finished dictates whether light is tapped into the stone, reflected around inside, and returned to the eye. A well-cut gem channels most of the light back through the top, creating strong brilliance—the bright white sparkle—and, with dispersion, fire—the colored flashes. If the angles are too deep or too shallow, or the symmetry and polish are off, light escapes from the sides or bottom instead of exiting through the crown, making the stone look dull. Size, color, and clarity influence appearance in other ways, but the cut is what directly controls light performance, and thus the overall sparkle.