In the Winter 1985 Lab Notes section, John Koivula described a "piggyback" yellow diamond: two diamonds mounted together to create the illusion of a larger stone. (Dr. Max Bauer referred to such stones as "genuine doublets" in his 1904 book Precious Stones.) More than 20 years later, the GIA Laboratory recently had a chance to examine this same doublet again – as part of a unique, award-winning piece of jewelry designed by Virginia jeweler Charlie Kingrea (figure 1).

Although we could not remove the diamonds from their mountings, we were able to examine them more carefully this time and, specifically, to determine the origin of their deep yellow color. As reported in the 1985 Lab Note, the top diamond weighed 4.72 ct and measured 17.50 × 12.55 × 2.46 mm deep; the bottom one weighed 2.41 ct and measured 12.50 × 7.23 × 4.48 mm deep. We observed a dull, chalky green reaction to long-wave ultraviolet radiation, and a short-wave reaction that was similar but weaker. The color distribution seemed even, but because of the flatness of the two pieces, uneven color distribution would have been difficult to observe. Both stones showed a 415 nm line in the desk-model spectroscope, with the 503 nm pair (496 and 503 nm) and a distinct 595 nm line indicating that they had been irradiated and annealed.