The Cut Grading Tool is a free Digital Gemology tool that grades a round brilliant diamond's cut from its proportions. It reads GIA's published cut grade estimation tables; it is for education and does not give a GIA grade.
In more detail
The tables hold 14,652 graded cells: 18 table sizes, each a grid of 37 crown by 22 pavilion angles. Table sizes run from 50% to 67%. The grade is the worst of the grid cell, the limits on the other proportions, and the finish grades. Digital Gemology is not affiliated with GIA.
How we measure it
We read the tables from the vector data of the published document, with no interpolation. Brilliance is traced on the T73; fire and scintillation are modeled, not traced. It shows 815 light maps: one per crown and pavilion cell at a 53% table, and the T73 as cut.
Related terms
- Cut grade: The cut grade rates how well a diamond's proportions and finish work, from Excellent to Poor. GIA gives it only to standard round brilliants in the D-to-Z color range.
- Brilliance: Brilliance is the white light that a cut stone returns to the viewer. In our census, it is the share of entering light that leaves through the crown toward the viewer.
- Light map: A light map is a face-up picture of a cut stone, colored by the direction each point's light came from. Red is direct light, green is indirect light, blue is contrast, and a dark color is leakage.
- Crown angle: The crown angle is the slope of the bezel facets, measured against the plane of the girdle.
- Pavilion angle: The pavilion angle is the slope of the pavilion mains, measured against the plane of the girdle.
- T73 benchmark: The T73 benchmark is the round brilliant that our tools compare every cut with, in the same gemstone. It has Tolkowsky's 1919 angles and table, and 73 facets: 57 plus 16 girdle facets.