A diamond brilliant’s beauty is the result of a complex combination of angles and proportions. In this article, Richard Liddicoat shows gemologists how to become familiar with how variations in cutting angles can affect a diamond’s face-up appearance. Using Marcel Tolkowsky’s ideal cut as a point of reference, Liddicoat presents techniques for estimating a particular diamond’s proportion values, describing how variables such as pavilion depth and size of table reflection influence the overall look and quality of a round brilliant.