Drag to rotate · pinch or Ctrl + scroll to zoom · tap a part
Rotate the ring, explode it into its parts and tap a part to learn what it does. Then change the diamond's proportions and symmetry and see how GIA's published standards treat them.
A slice through the middle of the stone. Light falls straight down onto the top. Inside, it bounces off the pavilion only when it meets a facet at more than diamond's critical angle (24.4°, from its refractive index of 2.417). Too shallow or too deep, and light escapes through the bottom instead of coming back to the eye.
GIA grades the cut of a round brilliant Excellent, Very Good, Good, Fair or Poor. The grade comes from seven components, and the stone gets the lowest of them: one weak point is enough to lower the whole grade.
Modelled by GIA with ray tracing and checked by observers.
Girdle thickness and culet size feed in here.
Only Excellent or Very Good symmetry meet GIA's criteria for an Excellent cut. Try the symmetry lab below.
Your proportions against GIA's published ranges for Excellent
| Parameter | This stone | Excellent range |
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Being inside every range is necessary but not enough. GIA notes that no single measurement predicts the grade: parameters can combine badly and lower it. For a real estimate, GIA offers its free Facetware cut estimator.
Symmetry measures how precisely the facets line up. GIA publishes exact limits for ten measurable faults. Move the sliders to add faults and watch the face-up view and the grade. The drawing magnifies faults five times so you can see them; real limits are tiny.
| Measured fault | Value | Grade on its own |
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Sources