Tacori Diamonds Details
Diamonds are usually cut into brilliants to bring out their brilliance, the amount of light reflected back to the viewer, and fire, the degree of colorful prismatic flashes seen. Both properties are strongly affected by the cut of the stone, but they are a function of diamond's high refractive index (RI; the degree to which incident light is bent upon entering the stone) of 2.417 (as measured by sodium light, 589.3 nm) and high dispersion (the degree to which white light is split into its spectral colors within the stone) of 0.044, as measured by the sodium B and G line interval. Thus, if a diamond simulant's RI and dispersion are too low it will appear comparatively dull or "lifeless"; if the RI and dispersion are too high, the effect will be considered unreal or even tacky. Very few simulants have closely approximating RI and dispersion, but even the close simulants can be separated by an experienced observer. Direct measurements of RI and dispersion are impractical (a standard gemological refractometer has an upper limit of about RI 1.81), but several companies have devised reflectivity meters to gauge a material's RI indirectly by measuring how well it reflects an infrared beam.
Perhaps equally as important is optic character. Diamond and other cubic (and also amorphous) materials are isotropic, meaning light entering a stone behaves the same way regardless of direction. Conversely, most minerals are anisotropic which produces birefringence or double refraction of light entering the material in all directions other than an optic axis (a direction of single refraction in a doubly refractive material). Under low magnification, this birefringence is usually detectable as a visual doubling of a cut gemstone's rear facets or internal flaws. An effective diamond simulant should therefore be isotropic.
Diamonds are usually cut into brilliants to bring out their brilliance, the amount of light reflected back to the viewer, and fire, the degree of colorful prismatic flashes seen. Both properties are strongly affected by the cut of the stone, but they are a function of diamond's high refractive index (RI; the degree to which incident light is bent upon entering the stone) of 2.417 (as measured by sodium light, 589.3 nm) and high dispersion (the degree to which white light is split into its spectral colors within the stone) of 0.044, as measured by the sodium B and G line interval. Thus, if a diamond simulant's RI and dispersion are too low it will appear comparatively dull or "lifeless"; if the RI and dispersion are too high, the effect will be considered unreal or even tacky. Very few simulants have closely approximating RI and dispersion, but even the close simulants can be separated by an experienced observer. Direct measurements of RI and dispersion are impractical (a standard gemological refractometer has an upper limit of about RI 1.81), but several companies have devised reflectivity meters to gauge a material's RI indirectly by measuring how well it reflects an infrared beam.
Perhaps equally as important is optic character. Diamond and other cubic (and also amorphous) materials are isotropic, meaning light entering a stone behaves the same way regardless of direction. Conversely, most minerals are anisotropic which produces birefringence or double refraction of light entering the material in all directions other than an optic axis (a direction of single refraction in a doubly refractive material). Under low magnification, this birefringence is usually detectable as a visual doubling of a cut gemstone's rear facets or internal flaws. An effective diamond simulant should therefore be isotropic.
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