NEW SCREENING METHOD FOR YELLOW LAB-GROWN DIAMONDS

Recently GIA has been receiving increased amounts of yellow melee. Using traditional testing methods, this can be extremely challenging whilst meeting strict deadlines. A proposed method to aid in the filtering of synthetics from natural diamonds involves the use of X-ray fluorescence.

X-ray fluorescence is commonly used in the mining industry. It can become a valuable asset used as a gemmological tool for diamonds. Natural Ib yellow diamonds remain inert when subjected to UV or X-ray exposure. While HPHT yellow lab-grown diamonds fluorescence green under UV and X-ray exposure. Using this stark contrast, yellow HPHT lab-grown diamonds can be quickly identified in “salted” batches of yellow melee.

A PF-100 Verifier was used to conduct this experiment. Large batches of yellow melee were loaded on to a tray. The melee were exposed for a few brief seconds to approximately 90 kv and 3.2 mA. The recorded X-ray fluorescence was imaged. All samples exhibiting green fluorescence were confirmed to HPHT Lab-grown.

The cause of this green fluorescence is currently under investigation. It is suggested that the cause of this green fluorescence is due to Nickel related features. Nickel is a commonly used catalyst during HPHT growth. Using a combination of spectroscopic tools, we identified a series of features common within all HPHT yellow lab grown diamonds. These features can be used to assist in screening out HPHT yellow lab-grown diamonds.