“EX Level”Specification on Inclination of Upper and Lower Girdle Facets of Round Brilliant Cut in New GIA Cut Standard

Inclinations of upper girdle and lower girdle facets are two important parameters of round brilliant cut.This paper provides specifications on inclinations of upper girdle and lower girdle facets for Gemological Institute of America（GIA）“EX level”.Furthermore，the specifications are visual by mathematical methods and computer software（e.g.Pro/E，Matlab and MathCAD）.Finally，some data of sample provided by the relevant literature are visualized and parameterized.The method has guiding significance for the design of round brilliant cut gemstone，processing and testing the finished product.