Ask whether the stone was treated after growth: roughly 80% of CVD diamonds submitted to GIA since 2020 had undergone post-growth processing, and an IGI report notes treatment only when someone asks for it.

That is one of eleven questions worth putting to any seller before you buy a laboratory-grown diamond above five carats. Each one is here because a buyer has asked it, or should have. Each comes with what a good answer sounds like and what a bad one sounds like.

We wrote this so you could use it on anyone, including us. The questions whose answers are uncomfortable for sellers are the ones most worth asking, so the most uncomfortable one comes first.

It is the question behind every version of “am I about to be taken?”, so it comes first.

The honest answer is no, and a seller who tells you otherwise is saying something the price record contradicts. Laboratory-grown wholesale prices fell more than 97 percent between mid-2018 and mid-2026, by Edahn Golan Diamond Research’s measure. In 2025 De Beers, whose core business is natural diamonds, closed its own laboratory-grown brand, Lightbox, its chief executive citing “the persistently declining value of lab-grown diamonds.”

Buy a large laboratory-grown diamond for what it is to wear, at a fair price for today. Our guide to what a large stone actually costs shows how to judge that price.

Most CVD stones are, and the report won’t say so unless someone asked.

Roughly 80 percent of the CVD diamonds submitted to GIA since 2020 had undergone post-growth processing, usually to remove brown. At record sizes, GIA has also seen stones grown slowly enough to need no treatment, so don’t assume either way. Treatment is permanent and not a defect: the point of asking is disclosure, not avoidance.

Boron is blue nuance before you can see it.

In its 2017 review, GIA found that a majority of the colorless HPHT samples it examined were Type IIb, carrying boron. CVD stones are typically Type IIa. Our guide to diamond type explains why that matters.

Video alone rarely settles cut. As one buyer put it: “I really can’t tell anything from the videos.”

Our guide to why cut is the hard part covers what the proportions and images should show.

Price per carat falls above five carats, and most sellers won’t volunteer it.

On September 18, 2026, one marketplace listed a 5.01-carat D/VVS2 at $1,136 per carat and a 10.02-carat D/VVS2 at $735. Our guide to what a large stone actually costs has the full dated comparison.

It is the largest single component of a retail price, and almost no one publishes it.

Edahn Golan Diamond Research puts the typical retail markup on a loose laboratory-grown diamond at 250 to 300 percent: a retail price three and a half to four times what the retailer paid.

Cut is where large stones differ most, and the paperwork is thinnest.

GIA’s laboratory-grown assessment grades cut for round brilliants only. Not every IGI report for a fancy shape carries a cut grade, and GCAL’s 8X does not yet cover emerald cuts.

“Certified” means nothing until you have checked it.

An IGI report can be checked free at lookup.igi.org against the inscription on the girdle. Our guide to certification and verification walks through it.

For a stone at this size, an independent look costs little relative to the price.

Independent escrow is one route: on a $100,000 purchase it costs about $1,900, under 2 percent of the price.

Those are two different remedies, and most sellers publish only the first.

The terms vary more than buyers expect. As of September 2026, one major seller issues store credit only on returns above $15,000 and excludes stones over five carats from returns entirely; another charges a 20 percent restocking fee on loose diamonds.

Cutting decides how a large stone looks, and a seller who knows can tell you.

Some sellers answer it in detail: one names Belgian master cutters in their fourth generation, another a New York workshop, and a natural-diamond house names South Africa, Botswana, New York and Antwerp.

Frequently asked questions