Moscow: Russian lab-grown diamond manufacturer New Diamond Technology says it has grown a 5.11 ct. K SI diamond, which it bills as the largest man-made polished near-colorless stone ever produced.

The manufacturer says the unenhanced radiant-cut type IIa diamond, produced by the high-pressure high-temperature (HPHT) method, bears a K SI grade but it has not yet been sent to a lab, according to company president Tamazi Khikhinashvili.

Experts familiar with diamond growing say that while growing a stone of that size is an impressive achievement, they wonder how repeatable the stone’s production is and note the reported color and clarity could be a hard sell commercially.

NDT has what it calls a “new approach” that lets it produce lab-grown gems with higher colors and clarity from its factories in Russia and Hong Kong. It produces gems ranging from 4 cts. to 11 cts. in rough, some of which fall into the 1 ct. to 4 cts. range in polished. Colors range from D to H, and clarities from IF to SI2.

The diamond’s size tops the 3.04 ct. round grown by Pure Grown Diamonds (formerly Gemesis), which that company regularly bills as the world’s largest man-made stone. Pure Grown’s IGI-graded I color, SI1 clarity very-good cut stone sells for $23,012 on its site. (Pure Grown also unveiled a 3 ct. K SI stone last summer.)

Khikhinashvili declines to say how the prices of his product compare to natural diamonds, but says they are “more affordable.” He says the company has sold to customers in Europe, Asia, and the United States.