Editor’s Note
This article examines the delicate nature of polki diamonds and the growing market trend of filling them with high-refractive-index glass to enhance clarity and durability.
The term “polki” refers to a flat-cut diamond, a simple and ancient form of today’s “rose cut,” popular in traditional Indian kundan-meena jewelry. As most commercial-quality polkis are fashioned from flat rough crystals (e.g., macles) or chips from cutting larger crystals, they often contain surface-reaching cleavages or fissures, making them delicate. Over the past decade, the trade has seen an influx of polkis filled with high-refractive-index glass to improve clarity and durability, widely used in kundan-meena jewelry.
Recently, the Gem Testing Laboratory (GJEPC) in Jaipur received three light gray to brown polki-cut diamonds with square profiles for identification (Figure 1). They weighed 0.27–0.29 ct and measured 6.86–7.41 mm long and 0.36–0.41 mm thick. The client claimed they were natural but inquired about possible glass filling.
Initial microscopic examination revealed glass filling in all three samples, evidenced by color flashes (typically blue, violet, and pink) along cleavages and fissures (Figure 2). Some crackling effects were observed within fissures and cleavage planes intersecting at nearly 90° (octahedral cleavage in diamond). Energy-dispersive X-ray fluorescence (EDXRF) analyses further confirmed the presence of glass containing lead and bromine. The polkis also displayed dark brown grains, some associated with stress cracks, though these were not identified.
Given past experiences with square-profile polkis, further tests were conducted to determine natural or synthetic origin. Under crossed polarizers, all three displayed a checkerboard strain pattern from the top and sub-parallel columnar patterns from the sides. Infrared spectra confirmed them as type IIa diamonds. DiamondView imaging showed orange fluorescence, but no distinct growth patterns were resolved, and no phosphorescence was detected.
Photoluminescence spectra using 532 nm laser excitation revealed a distinct silicon vacancy–related peak at ~737 nm, even at room temperature (Figure 3). This feature is widely used by gemological laboratories to identify synthetic diamonds (both CVD- and HPHT-grown).
While glass-filled polki-cut diamonds and CVD synthetic diamonds fashioned as polkis have been encountered separately, this is the first reported case of glass-filled CVD synthetic diamond polkis, though their market penetration is unknown.
Polkis are typically fashioned from flat rough or chips, resulting in triangular or irregular profiles. The square profile of these samples is notable. Square-shaped polkis offer the best yield for crystals with square profiles, such as natural cubic crystals or CVD-grown synthetic diamonds, which exhibit a square, tabular habit. This feature can be useful in raising doubts, especially when such stones are mixed in parcels of polki-cut natural diamonds.
