Lab Notes Gems & Gemology, Spring 2022, Vol. 58, No. 1

Unusual Laser Drill Holes in a Laboratory-Grown Diamond

Laboratory-grown diamond contains a flux inclusion and laser drill holes.
Figure 1. Flux inclusion in a laboratory-grown diamond connected to a laser drill hole. Photomicrograph by Najmeh Anjomani; field of view 3.57 mm.

Diamonds with dark inclusions have been laser drilled to enhance their clarity for more than 60 years. The internal inclusion is drilled from the diamond surface and then acid-boiled to bleach it out. GIA has identified many natural diamonds treated by this technique, but the Carlsbad laboratory recently received for a colored diamond identification and origin report an undisclosed laboratory-grown diamond with unusual laser drill holes.

The diamond was a Fancy yellow cushion modified brilliant weighing 2.02 ct. Gemological and spectroscopic analysis confirmed it was an HPHT-grown synthetic diamond. The diamond was attracted to a small magnet due to the numerous metallic inclusions. No strain was visible under crossed polarizers, and DiamondView imaging showed the typical cuboctahedral HPHT growth pattern.

Clarity was low due to the presence of numerous large flux inclusions, so laser drilling was likely done to enhance the appearance and clarity. One of the laser drill holes connected to a large flux inclusion can be seen in figure 1. A metallic flux inclusion cannot be bleached as some mineral inclusions can and so it must be dissolved out, which could pose additional challenges to improving the clarity. It appears there was an unsuccessful attempt to remove the flux, as the inclusion was still eye visible.

This laboratory-grown diamond features unusual laser drill holes.
Figure 2. Clusters of unusual laser drill holes in a laboratory-grown diamond. Photomicrographs by Najmeh Anjomani; fields of view 3.57 mm (left) and 2.61 mm (right).

Three clusters of intersecting laser drill tubes resembling corals were observed (figures 2 and 3). We could see numerous roundish openings on the surface filled with dark materials. Raman spectroscopy confirmed they were all non-diamond carbon materials. Here the laser beam was likely reflected off a flux inclusion and refocused to a new point farther than intended, resulting in the unusual branching pattern. Other flux inclusions could have been successfully dissolved by acid because they were smaller than the one in figure 1 or because there were more drilled tubes for the acid to enter. This may have caused the unique crossed tubes inside the stone. Burn marks on the surface next to some of the laser drill holes might have been due to the heat generated by the laser beam (figure 3).

Laser drill holes and a burn mark, possibly from the laser.
Figure 3. Burn mark on the surface next to laser drill holes. Photomicrograph by Najmeh Anjomani; field of view 2.01 mm.

This diamond was identified as a laboratory-grown diamond. It was issued a laboratory-grown colored diamond report stating, “Laser drill holes are present.”

Najmeh Anjomani is a senior staff gemologist, and Troy Ardon is a senior research associate, at GIA in Carlsbad, California.