The author recently examined a 0.5 ct pear-shaped ruby measuring 6 × 4 mm that contained twinning planes and hollow channels known as Rose channels (see above). Because the Rose channels were hollow and empty, they had a refractive index of 1 (the RI of air), while the RI of the surrounding host ruby was 1.76–1.77. The contrasting refractive indices resulted in high optical relief, making the Rose channels easily visible. These linear inclusions are common in natural corundum and were once thought to be boehmite needles (F. Notari et al., “‘Boehmite needles’ in corundum are Rose channels,” Fall 2018 G&G, p. 257).
The author recently examined a 0.5 ct pear-shaped ruby measuring 6 × 4 mm that contained twinning planes and hollow channels known as Rose channels (see above). Because the Rose channels were hollow and empty, they had a refractive index of 1 (the RI of air), while the RI of the surrounding host ruby was 1.76–1.77. The contrasting refractive indices resulted in high optical relief, making the Rose channels easily visible. These linear inclusions are common in natural corundum and were once thought to be boehmite needles (F. Notari et al., “‘Boehmite needles’ in corundum are Rose channels,” Fall 2018 G&G, p. 257).