The Carlsbad laboratory recently examined a yellow-green hexagonal prismatic crystal (figure 1, left) that was presented as sapphire. The rough specimen was approximately 11 mm long. The specific gravity was measured as 4.00, and the stone was inert to both long- and short-wave UV. The identity of the rough sapphire was confirmed by Raman spectroscopy. Microscopic examination revealed that the stone was partially covered by drops of green glassy residue, and numerous fractures throughout it were filled with the same material. Also observed were numerous trapped gas bubbles and a prominent orange flash effect, consistent with a lead-glass filling (figure 1, right). Energy-dispersive X-ray fluorescence (EDXRF) analysis confirmed the presence of lead.
Laser ablation–inductively coupled plasma–quadrupole mass spectrometry (LA-ICP-MS) was used to investigate the chemical composition of the green glassy residue. A line of ablation spots, positioned on one of the flat crystal faces, was designed to cross a large drop of the residue. The oxide weight percent profile (figure 2, left) revealed that the residue contained 9.3 to 9.7 wt.% B2O3, 23.7 to 24.9 wt.% Al2O3, 12.2 to 12.6 wt.% SiO2, 3.6 to 4.2 wt.% CuO, 1.2 to 1.3 wt.% CdO, and 45.4 to 47.4 wt.% PbO. The combined oxide weight percent of Li, Na, K, Ca, and Zr was around 1.5 (averaged value). The chemical analysis confirmed that the filler was lead glass.
With such a small amount of Al (2.6 wt.% Al2O3) in the lead glass (Z.Q. Zeng and P. Hing, “Preparation and thermal expansion behavior of glass coatings for electronic applications,” Material Chemistry and Physics, Vol. 75, No. 1–3, 2002, pp. 260–264), the approximate composition of major elements can be obtained by subtracting 24.22 wt.% Al2O3 (arising from the host sapphire crystal) from the total chemical composition and renormalizing the sum to 100 wt.% oxide (R. Barbour, Glassblowing for Laboratory Technicians, Wellington, New Zealand, Pergamon Press, 1978, p. 4). The renormalized composition of the lead glass was 63.3 wt.% PbO, 16.9 wt.% SiO2, 12.8 wt.% B2O3, 5.3 wt.% CuO, and 1.7 wt.% CdO. The PbO wt.% was plotted on the Pb wt.% oxide vs. refractive index plot (http://physics.info/refraction) and showed an RI of 1.75, which is very close to corundum’s RI of 1.76–1.77 (figure 2, right). The high refractive index of the glass concealed the difference in luster between corundum and filler.
A previous study reported on blue cobalt-colored lead glass–filled sapphires whose color was assigned to the presence of a small amount of cobalt in the filler (T. Leeawatanasuk et al., “Cobalt-doped glass-filled sapphire; an update,” Australian Gemmologist, Vol. 25, No. 1, 2013, pp. 14–20). The green color of the glass in this specimen was likely caused by the combination of CuO (which causes a greenish blue color in glass) and CdS (which causes a yellow color; see B.H.W.S. De Jong et al., “Glass,” in Ullmann’s Encyclopedia of Industrial Chemistry, Wiley-VCH, 2000, http://dx.doi.org/10.1002/14356007.a12_365). The yellowish appearance and the high levels of Fe (1629 to 2640 ppmw) in the area without filler indicate that the piece might have been a yellow sapphire before being filled. This was the first sapphire with green lead-glass filling examined at the Carlsbad laboratory.
The Carlsbad laboratory recently examined a yellow-green hexagonal prismatic crystal (figure 1, left) that was presented as sapphire. The rough specimen was approximately 11 mm long. The specific gravity was measured as 4.00, and the stone was inert to both long- and short-wave UV. The identity of the rough sapphire was confirmed by Raman spectroscopy. Microscopic examination revealed that the stone was partially covered by drops of green glassy residue, and numerous fractures throughout it were filled with the same material. Also observed were numerous trapped gas bubbles and a prominent orange flash effect, consistent with a lead-glass filling (figure 1, right). Energy-dispersive X-ray fluorescence (EDXRF) analysis confirmed the presence of lead.
Laser ablation–inductively coupled plasma–quadrupole mass spectrometry (LA-ICP-MS) was used to investigate the chemical composition of the green glassy residue. A line of ablation spots, positioned on one of the flat crystal faces, was designed to cross a large drop of the residue. The oxide weight percent profile (figure 2, left) revealed that the residue contained 9.3 to 9.7 wt.% B2O3, 23.7 to 24.9 wt.% Al2O3, 12.2 to 12.6 wt.% SiO2, 3.6 to 4.2 wt.% CuO, 1.2 to 1.3 wt.% CdO, and 45.4 to 47.4 wt.% PbO. The combined oxide weight percent of Li, Na, K, Ca, and Zr was around 1.5 (averaged value). The chemical analysis confirmed that the filler was lead glass.
With such a small amount of Al (2.6 wt.% Al2O3) in the lead glass (Z.Q. Zeng and P. Hing, “Preparation and thermal expansion behavior of glass coatings for electronic applications,” Material Chemistry and Physics, Vol. 75, No. 1–3, 2002, pp. 260–264), the approximate composition of major elements can be obtained by subtracting 24.22 wt.% Al2O3 (arising from the host sapphire crystal) from the total chemical composition and renormalizing the sum to 100 wt.% oxide (R. Barbour, Glassblowing for Laboratory Technicians, Wellington, New Zealand, Pergamon Press, 1978, p. 4). The renormalized composition of the lead glass was 63.3 wt.% PbO, 16.9 wt.% SiO2, 12.8 wt.% B2O3, 5.3 wt.% CuO, and 1.7 wt.% CdO. The PbO wt.% was plotted on the Pb wt.% oxide vs. refractive index plot (http://physics.info/refraction) and showed an RI of 1.75, which is very close to corundum’s RI of 1.76–1.77 (figure 2, right). The high refractive index of the glass concealed the difference in luster between corundum and filler.
A previous study reported on blue cobalt-colored lead glass–filled sapphires whose color was assigned to the presence of a small amount of cobalt in the filler (T. Leeawatanasuk et al., “Cobalt-doped glass-filled sapphire; an update,” Australian Gemmologist, Vol. 25, No. 1, 2013, pp. 14–20). The green color of the glass in this specimen was likely caused by the combination of CuO (which causes a greenish blue color in glass) and CdS (which causes a yellow color; see B.H.W.S. De Jong et al., “Glass,” in Ullmann’s Encyclopedia of Industrial Chemistry, Wiley-VCH, 2000, http://dx.doi.org/10.1002/14356007.a12_365). The yellowish appearance and the high levels of Fe (1629 to 2640 ppmw) in the area without filler indicate that the piece might have been a yellow sapphire before being filled. This was the first sapphire with green lead-glass filling examined at the Carlsbad laboratory.
