DDG Ass #12 Key Terms PDF

DDG Ass #12 Key Terms: Average Girdle Diameter—The result achieved by adding the smallest and largest diameter measurements of a round brilliant and dividing by two. Crown Angle—The angle formed by the bezel facets and the girdle plane. Crown Height Percentage—The distance from the gird...

DDG Ass #12 Key Terms: Average Girdle Diameter—The result achieved by adding the smallest and largest diameter measurements of a round brilliant and dividing by two. Crown Angle—The angle formed by the bezel facets and the girdle plane. Crown Height Percentage—The distance from the girdle plane to the table, expressed as a percentage of average girdle diameter. Digging Out—Cutting technique that thins the area of the girdle where the upper half facet junctions meet the lower half facet junctions, to retain weight or remove clarity characteristics. Girdle Thickness—The width of a fashioned gem’s girdle. Painting—Cutting technique that thins the area of the girdle where the bezel and pavilion main meet, to retain weight or remove clarity characteristics. Star Length Percentage—The length of the star facets expressed as a percentage of the total distance between the girdle and the edge of the table facet. Table Gauge—A transparent measuring device divided into millimeters and tenths of a millimeter, used to measure a diamond’s table. Table Percentage—A diamond’s table size expressed as a percentage of its average girdle diameter. Total Depth Percentage—Table-to-culet depth, expressed as a percentage of average girdle diameter. Key Concepts Average girdle diameter is the basis for comparing a diamond’s other proportions. Diamonds are always measured in millimeters. Most round brilliants have table percentages that range from about 55 percent to about 65 percent. To determine a round brilliant diamond's table size, measure the table facet in four directions and average the measurements. With practice, table size estimation techniques can be quick and fairly accurate. A shallow crown can help a cutter save weight from shallow rough, but it can have a negative effect on appearance. A diamond’s girdle should be thick enough to prevent chipping, but not so thick that it detracts from the stone’s appearance. Severe painting and digging out result in hill positions of differing thicknesses and uneven scalloping around the girdle. Significant painting or digging out can give a diamond an unattractive scintillation pattern or make it appear darker.