Lab Notes Gems & Gemology, Fall 2025, Vol. 61, No. 3

Quench-Crackled and Dyed Laboratory-Grown Sapphire

Jamie Leigh Price

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Figure 1. Face-up appearance of a quench-crackled and dyed laboratory-grown colorless sapphire, measuring 13.10 × 12.73 × 7.51 mm. Photo by Adriana Gudino.
 
Figure 1. Face-up appearance of a quench-crackled and dyed laboratory-grown colorless sapphire, measuring 13.10 × 12.73 × 7.51 mm. Photo by Adriana Gudino.

One common process used to alter gemstones is the “quench-crackle and dye” treatment, in which a heated stone is quenched in room-temperature water, inducing fractures that allow dye to penetrate the stone and change the appearance of its color. This technique was introduced in the 1990s (S.F. McClure and C.P. Smith, “Gemstone enhancement and detection in the 1990s,” Winter 2000 G&G, pp. 336–359) and is typically applied to quartz, cubic zirconia, glass, and other synthetic gemstones due to their low cost and high availability.

Figure 2. A comparison of the Vis-NIR spectra of a natural colorless sapphire, a natural bluish green sapphire, and the bluish green laboratory-grown sapphire demonstrates that the color in the latter results from the dye seen in figure 3. Spectra are offset vertically for clarity.
 
Figure 2. A comparison of the Vis-NIR spectra of a natural colorless sapphire, a natural bluish green sapphire, and the bluish green laboratory-grown sapphire demonstrates that the color in the latter results from the dye seen in figure 3. Spectra are offset vertically for clarity.

The Carlsbad laboratory recently received a 12.65 ct laboratory-grown colorless sapphire that showed signs of treatment (figure 1). At first glance, the overall face-up color of this stone suggested it was a Paraíba tourmaline or a low-quality emerald. With the unaided eye, the color-causing dye-filled fractures were faintly visible. The refractive index, specific gravity, and other basic gemological tests identified the material as sapphire. Along with the lack of natural inclusions, testing with X-ray fluorescence revealed the absence of both gallium and iron, confirming that the stone was laboratory-grown. Visible/near-infrared (Vis-NIR) absorption spectroscopy displayed a broad band around 650 nm that did not match natural color-causing components found in corundum (figure 2). This explains the unnatural color of this sapphire. With a microscope, the fractures within this stone displayed characteristic weblike fractures induced by quenching. Unlike naturally occurring fractures, the fractures produced by this type of treatment have uniform spacing and depth, as shown in figure 3.

Figure 3. Dye concentrations along shallow, weblike induced fractures evenly spaced across the surface of a colorless laboratory-grown sapphire. Photomicrograph by Jamie Price; field of view 5.50 mm.
 
Figure 3. Dye concentrations along shallow, weblike induced fractures evenly spaced across the surface of a colorless laboratory-grown sapphire. Photomicrograph by Jamie Price; field of view 5.50 mm.

Jamie Leigh Price is a staff gemologist at GIA in Carlsbad, California.