The Carlsbad laboratory received two diamonds grown by the high-pressure, high-temperature (HPHT) process that contained interesting color zonation. The 0.51 ct round brilliant (figure 1, left), submitted for a laboratory-grown colored diamond report, received a Fancy Deep bluish green color grade. The 1.56 ct marquise (figure 1, right), submitted for the same LG-CD service, was Fancy black. Both stones were determined to be artificially irradiated. The high concentration of defects created by laboratory irradiation led to extensive absorption in the marquise, causing a black appearance that is fairly uncommon for laboratory-grown diamonds. When viewed through the pavilion, sector-dependent color zonation was visible in both stones (figure 2).
Dramatic color zonation corresponding with growth sectors is a feature of some fancy-color HPHT-grown diamonds (J.E. Shigley et al., “Gemesis laboratory-created diamonds,” Winter 2002 G&G, pp. 301–309; J.E. Shigley et al., “Lab-grown colored diamonds from Chatham Created Gems,” Summer 2004 G&G, pp. 128–145; S. Eaton-Magaña et al., “Observations on HPHT-grown synthetic diamonds: A review,” Fall 2017 G&G, pp. 262–284; Winter 2023 Lab Notes, pp. 489–490). In these particular irradiated stones, the areas of transmitted blue color were due to the GR1 defect, which created absorption primarily in the red portion of the visible spectrum (e.g., C.D. Clark et al., “The absorption spectra of natural and irradiated diamonds,” Proceedings of the Royal Society of London A: Mathematical, Physical, and Engineering Sciences, Vol. 234, No. 1198, 1956, pp. 363–381). Nitrogen can cause absorption in the blue portion of the visible spectrum to contribute to yellow color in some of the growth sectors, and together these can lead to a combined green color. From the pavilion of the round brilliant diamond (figure 2, left), the yellow sectors appeared to be distinct from blue, but these color components combined to appear green face-up (figure 1, left). Similarly, green coloration resulting from yellow Ib and blue IIb sectors was described in some early HPHT-grown diamonds (Shigley et al., 2004).
These stones offer examples of fun and distinctive features that can be observed in laboratory-grown colored diamonds.
The Carlsbad laboratory received two diamonds grown by the high-pressure, high-temperature (HPHT) process that contained interesting color zonation. The 0.51 ct round brilliant (figure 1, left), submitted for a laboratory-grown colored diamond report, received a Fancy Deep bluish green color grade. The 1.56 ct marquise (figure 1, right), submitted for the same LG-CD service, was Fancy black. Both stones were determined to be artificially irradiated. The high concentration of defects created by laboratory irradiation led to extensive absorption in the marquise, causing a black appearance that is fairly uncommon for laboratory-grown diamonds. When viewed through the pavilion, sector-dependent color zonation was visible in both stones (figure 2).
Dramatic color zonation corresponding with growth sectors is a feature of some fancy-color HPHT-grown diamonds (J.E. Shigley et al., “Gemesis laboratory-created diamonds,” Winter 2002 G&G, pp. 301–309; J.E. Shigley et al., “Lab-grown colored diamonds from Chatham Created Gems,” Summer 2004 G&G, pp. 128–145; S. Eaton-Magaña et al., “Observations on HPHT-grown synthetic diamonds: A review,” Fall 2017 G&G, pp. 262–284; Winter 2023 Lab Notes, pp. 489–490). In these particular irradiated stones, the areas of transmitted blue color were due to the GR1 defect, which created absorption primarily in the red portion of the visible spectrum (e.g., C.D. Clark et al., “The absorption spectra of natural and irradiated diamonds,” Proceedings of the Royal Society of London A: Mathematical, Physical, and Engineering Sciences, Vol. 234, No. 1198, 1956, pp. 363–381). Nitrogen can cause absorption in the blue portion of the visible spectrum to contribute to yellow color in some of the growth sectors, and together these can lead to a combined green color. From the pavilion of the round brilliant diamond (figure 2, left), the yellow sectors appeared to be distinct from blue, but these color components combined to appear green face-up (figure 1, left). Similarly, green coloration resulting from yellow Ib and blue IIb sectors was described in some early HPHT-grown diamonds (Shigley et al., 2004).
These stones offer examples of fun and distinctive features that can be observed in laboratory-grown colored diamonds.