Figure B-2. These diamonds are viewed negatively by experienced members of the diamond trade, due to a variety of unattractive pattern-related traits such as a fisheye (left), dark upper-girdle facets (center), and a busy, broken overall pattern (right). Photos by A. Gilbertson and B. Green.
Figure 2. A round brilliant cut diamond can be described using eight proportion parameters: table size, crown angle, pavilion angle, star facet length, lower-girdle facet length, girdle thickness, culet size, and number of girdle facets.Other parameters (e.g., crown height) can be calculated fromthese eight. (A) All linear distances in this profile view can be described as a percentage of the girdle diameter, although at the GIA GemLaboratory girdle thickness and culet size are described verbally based on a visual assessment. (B) In this face-up view of the crown, the star facet length is shown at 50%, so that the star facets extend half the distance fromthe table to the girdle (indicated here by 0–1). (C) In this table-down view of the pavilion, the lower-girdle facet length is shown at 75%, so that the lower-girdle facets extend three-fourths of the distance fromthe girdle to the culet center (0–1). Adapted fromReinitz et al. (2001).
Figure 1. The round brilliant is themes popular diamond cut. Because of its popularity, assessment of this cut has been the subject of considerable research. This image shows a wide range of uses for this style in commercial jewelry, as well as loose polished diamonds and diamond crystals. The loose polished diamonds weigh 1.05–3.01 ct, and the rough crystals weigh 2.14–2.49 ct. Jewelry and loose polished diamonds courtesy of Ben Bridge Jewelers. Composite photo by Harold & Erica Van Pelt.
Figure 7. Shown here is a small assortment of the “patterned” hemispheres used in the testing of the brightness metrics. Inset:Using a hemisphere to observe diamonds. Photos by A. Gilbertson.
Figure 3. A diamond looks different in different lighting and viewing environments. In these images, the same diamond was photographed in diffused lighting (left),mixed lighting (center), and spot lighting only (right). Photos by A. Gilbertson.
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