Gem News International Gems & Gemology, Winter 2018, Vol. 54, No. 4

Single HPHT Synthetic Diamond Mixed in Natural Diamond Ring

Ring set with 194 natural diamonds and one HPHT-grown specimen
Figure 1. The ring with 194 natural diamonds and one HPHT-grown specimen. Photo by Nazar Ahmed Ambalathveettil.

Recently, a ring with 195 mounted colorless and near-colorless stones (figure 1) was submitted to Dubai Central Laboratory for identification. The ring contained round-brilliant-cut diamond melee arranged in rows. Testing with the DiamondSure instrument identified 194 of them as natural diamond, and the remaining melee was referred for further testing.

High reflection of metallic flux inclusions
Figure 2. These metallic flux inclusions that are associated with feathers show high reflection in oblique light. Photo by Nazar Ahmed Ambalathveettil.
The yellow fluorescence of the HPHT-grown diamond
Figure 3. The laboratory-grown diamond fluoresced yellow under long-wave UV (left) and greenish yellow under short-wave UV light (right). Photos by Nazar Ahmed Ambalathveettil.

The sample’s setting in the ring restricted us to FTIR spectroscopy in reflection mode to determine its identity. Solid metallic inclusions were revealed under the microscope (figure 2). The specimen displayed strong yellow and moderate greenish yellow fluorescence under long-wave UV and short-wave UV, respectively (figure 3). The inclusions and fluorescence suggested HPHT-grown diamond, which generally shows a stronger fluorescence reaction to short-wave UV than to long-wave UV. The vast majority of HPHT synthetics in the “colorless” range exhibit no detectable fluorescence to long-wave UV (S. Eaton-Magaña et al., “Observations on HPHT-grown synthetic diamonds: A review,” Fall 2017 G&G, pp. 262–284), but this one showed strong fluorescence under long-wave UV.

The stone was further examined with DiamondView imaging and photoluminescence (PL) spectroscopy. Strong yellowish green fluorescence and blue phosphorescence were observed with the DiamondView, but the growth sector pattern typical of HPHT-grown diamond was not visible because of the stone’s size. PL spectroscopy showed nickel-related peaks at 882/884 nm. Based on these results, we concluded that this was an HPHT laboratory-grown diamond.

We later learned that the customer had given the ring to a jewelry repair shop to replace a broken diamond, which may account for the single lab-grown specimen. This is a good example of the need for vigilance in every stage of diamond jewelry making.

Nazar Ahmed Ambalathveettil (, Nahla Al Muhari, and Sutas Singbamroong are affiliated with the Gemstone Unit, Dubai Central Laboratory in the United Arab Emirates.