gems, lapis lazuli, Afghanistan, dyed lapis lazuli

Over the years, the New York laboratory has been asked many times to check for dye and, more recently, for evidence of oil or paraffin in lapis lazuli (see, for example, Gem Trade Lab Notes section, Summer 1981 and Winter 1985). Heretofore, when acetone applied with a cotton swab has produced evidence of dye, the dye has been detected primarily in the cracks and porous areas of the stone. The effect of the dye is to darken light areas and provide a more uniform appearance. Some of the dyed stones are further “sealed” with some type of oil, wax, or the like. However, some paraffin-treated lapis (whether dyed or undyed) does “sweat” when tested with a thermal reaction tester. Recently, a strand of 7-mm violet-blue beads known to be dyed (figure 4) was donated to the laboratory. Unlike most of the dyed lapis we have examined, however, these beads were so heavily saturated that they virtually owed their color to dye. When exposed to long-wave ultraviolet radiation, some of the beads showed a patchy red fluorescence; with short-wave, only about half showed the chalky green fluorescence characteristic of natural lapis lazuli. Surprisingly, the “swab” test was not as revealing with these beads as with the previously described stones we have visually seen. However, the thermal reaction tester produced evidence of paraffin treatment, so it may be that the paraffin “seal” must be removed before the dye will stain the swab. Under magnification, a few of the beads showed purple dye in the cracks, while others showed the same unnatural purple color in patches not associated with cracks or otherwise obviously porous areas. Under a Chelsea color filter, the beads all appeared a definite brownish red, much brighter than any natural-colored specimens we have tested.