prior fluorescence studies performed at GIA found that about 35% of near-colorless gem diamonds fluoresce to long-wave UV radiation, with 97% of those diamonds showing blue fluorescence (Moses et al., 1997). However, colored diamonds more commonly show fluorescence, and in a wider variety of colors (e.g., figure 1). Given the methodology with which fluorescence is typically observed, it is sometimes difficult to determine the underlying mechanism of this behavior and, specifically, the influence of the natural, synthetic, or treated nature of the diamond on its fluorescence. Becquerel (1868) and Dyer and Matthews (1958) were among the first scientists to study the fluorescence properties of diamonds. Dyer and Matthews studied the luminescence of the 415.5 and 504.0 nm systems (now identified as the N3 and H3 defects; see, e.g., Collins, 1982a) and found that these features were related to blue and green fluorescence, respectively. A review by Fritsch and Waychunas (1994) detailed the observed fluorescence and phosphorescence of diamonds according to their bodycolor.