Lab Notes Gems & Gemology, Fall 2021, Vol. 57, No. 3

Laboratory-Grown Diamond with Internal Laser Markings

CVD-grown diamond with internal laser markings.
Figure 1. The 2.44 ct pear-cut CVD-grown diamond with internal spiral markings. Photo by Jian Xin Liao.

With the recent influx of laboratory-grown diamonds into the market and to aid consumer awareness of diamond origin, manufacturers are often marking their laboratory-created diamonds using internal inscriptions. The New York laboratory recently examined a 2.44 ct pear-shaped CVD (chemical vapor deposition) grown diamond with unusual internal spiral markings (figure 1).

Laser marking in a spiral shape.
Figure 2. Micro image of the largest spiral marking; the line thickness is 40 microns. Photomicrograph by Paul Johnson.

The three spiral markings were black and all in the same plane (i.e., at the same depth). The line thickness of these markings was about 40 microns (figure 2), whereas laser inscriptions are generally less than 20 microns. It was suspected that these markings were created by accidental laser damage rather than laser inscription. Raman mapping of the surface above the markings revealed a much broader diamond Raman peak compared to the rest of the crystal. This is the result of laser damage to the crystal lattice. Further Raman mapping using confocal settings identified a graphite peak at about 1620 cm–1. This offered proof that a laser, graphitizing the diamond, had created the markings.

The “inclusions” likely resulted from the laser marking the surface; this is done to provide a template to guide the polisher in producing the final shape. The intent would have been to score the surface; however, the laser appeared to have been inadvertently focused below the surface, resulting in the unusual internal markings.

As the markings are internal and graphitized, they are considered clarity features. The clarity grade was determined to be SI1, followed by a report comment stating, “Clarity grade is based on manufacturing remnants that are not shown.”

Paul Johnson is manager of analytics, Stephanie Persaud is research associate, and Cori Bulgrin is supervisor of training, at GIA in New York.