How Large Lab-Grown Diamonds Are Actually Made

The largest polished laboratory-grown diamond ever certified is 75.33 carats, grown by CVD from a 190-carat rough over roughly 270 days and unveiled in May 2024 — and none of the record stones with a published clarity grade, including the 50.25-carat certified in 2023 at G/VS2, is Internally Flawless.

Named the Celebration of India, the square emerald-cut stone was grown by Ethereal Green Diamond LLP in collaboration with RockRush. IGI announced its grading on May 30, 2024, and the stone went on display at JCK Las Vegas the following day. IGI graded it as Type IIa with Excellent polish and symmetry; the announcement gave no color or clarity grade. Cutting and polishing took about 30 days.

This Operia guide sets out the records in order, explains why size is physically hard to grow, and shows where large laboratory-grown diamonds actually become scarce.

How have the records progressed?

Two weights circulate for every large diamond, and they measure different things. Rough weight is the crystal as it leaves the growth chamber; polished weight is what remains after cutting. The 75.33-carat record kept about 40 percent of its 190-carat rough. The 50.25-carat Shiphra kept about a third of its 150-carat rough. Every figure on this page is labeled as one or the other.

Selected polished records

Dashes mark details not included in the laboratory or grower announcement.

GIA noted that the 16.41-carat stone had not been treated after growth to improve its color. The 50.25-carat Shiphra was grown over about eight months and cut in Surat; Tehmasp Printer, president of IGI India, called it “a paradigm-shifting breakthrough, surpassing 50 carats.” It was bought by Shiphra Jewelry, which gave the stone its name.

The rate of change is the striking part. Dr. Wuyi Wang, GIA’s vice president of research and development, has noted that the first CVD diamond he examined, in 2003, was a 0.23-carat brown pear shape. GIA has described the faceted-size benchmark as rising more than fourfold since early 2022.

Rough crystal records

The heaviest rough crystal records are a separate list, and they are routinely confused with the polished records. They include a 150.42-carat blue HPHT crystal produced by Alkor-D and Meylor Global in November 2021 and a 141.58-carat gray crystal; before them, a 115-carat HPHT crystal held the record. These are weights of uncut crystals and cannot be compared with the polished weights above.

Why is size so hard to grow?

CVD builds diamond upward from a thin diamond seed plate, layer by layer. Three limits make large stones slow and difficult.

Even well-grown CVD diamond carries threading dislocations, line defects that run through the crystal, at typical densities of 10⁴ to 10⁶ per square centimeter. This is why the record stones took months rather than weeks: the 75.33-carat stone’s rough grew for roughly 270 days, the 50.25-carat stone’s for about eight months.

Why does CVD hold the large-stone records?

HPHT, the other growth method, reproduces the conditions under which natural diamond forms: temperatures of 1,300 to 1,600°C and pressures above 870,000 psi. GIA likens the 5 to 6 gigapascals involved to “a commercial jet airplane balanced on a fingertip.” Crystallization takes days to weeks.

HPHT has produced very large rough crystals, but most faceted HPHT stones weigh under 2 carats. At large polished sizes the balance reverses: among stones of 4 carats and above submitted to GIA, CVD substantially outnumbers HPHT, and every polished record in the table above is CVD. One difference is time. CVD growth can be sustained for months, where HPHT crystallization runs for days to weeks.

Where do large lab-grown diamonds actually thin out?

GIA’s analysis of the laboratory-grown diamonds of 4 carats and above submitted to it shows two things. Most arrived in 2021 or later, and the majority weigh between 4 and 5 carats. Above 5 carats, the numbers fall away steeply.

The record stones sit at the far end of that tail. A 5-carat stone is already past the point where most large laboratory-grown diamonds stop.

What does this mean for what you can buy?

The record stones are individual showpieces. Each was announced by a laboratory and shown at a trade fair, and the 50.25-carat Shiphra went to the jewelry brand that named it. They mark what growers can achieve, not what is in stock.

For a buyer, three questions matter more than the record. Is a quoted weight polished or rough? Was the stone grown by CVD or HPHT? And what are its color and clarity grades? Size and top grades don’t arrive together automatically: every record stone with a published grade sits at G or H color, with VS2 or VVS2 clarity.

Above 5 carats, supply thins sharply, so choice at that size is narrower than the headlines about 50- and 75-carat stones suggest.

The Operia Standard

D-E color | VS1+ clarity | Excellent Cut/Polish.Symmetry 
Operia’s catalog sits in that tail by design: 5 to 10 carats, D and E color, VS1 clarity or better, with Excellent cut, polish and symmetry.

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