The Essential 7C's
During the 1980s in Japan, it was discovered that when a round brilliant diamond with exceptional symmetry was viewed from the bottom through a special viewer a pattern of hearts could be seen, and when viewed from the top showed eight gray arrowheads. Diamonds displaying such exceptional symmetry account for less than 1 % of all diamonds cut. The highest grades of polish, symmetry and perfect cutting angles allow it to reflect more light than a standard cut diamond.
Following the discovery, a special viewer was developed to display the Hearts & Arrows effect. The viewer is useful in determining the optical symmetry of a diamond, through the internal movement of light and reflection, depending on the size, shape and arrangement of facets. This optical symmetry is different from the Symmetry Grading on a laboratory grading report that assesses the 'tidiness' of facet intersections and placement. Diamonds with Hearts and Arrows patterns became very popular in Japan and spread as a trend in the USA during the mid 1990s.