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Lab-grown diamonds have become one of the fastest-growing categories in jewellery, and buyers arriving at the counter in 2026 are more informed than any generation before them. They know their 4Cs, they have done their research, and increasingly they are asking one specific question: Should I be looking for IGI or GIA certification for my lab-grown diamond?
It is a genuinely important question, and the answer has become more nuanced recently. GIA, the most recognised name in diamond grading, made significant changes to its lab-grown diamond certification. Those changes have shifted buying behaviour across the industry. If you are shopping without knowing what is shifted and why, you may struggle to compare stones accurately or understand what you are actually receiving.
This guide explains what each certification means, what GIA changed, and what most buyers are choosing today.
A diamond certificate is an independent document produced by a gemological laboratory that has physically examined the stone and recorded its characteristics under controlled conditions. For lab-grown diamonds specifically, that document carries enormous practical weight.
Unlike natural diamonds, where geological rarity forms part of the value story, lab-grown diamonds are assessed almost entirely on their graded quality. Without an independent certificate, you are relying entirely on the retailer's word. With one, you have a verified record from a qualified third party.
Certification protects buyers in several concrete ways:
It confirms the four Cs: cut, colour, clarity, and carat weight, independently verified
It supports accurate pricing comparisons, since two stones that appear similar can differ significantly on a grading scale.
It provides documentation for insurance purposes, which most insurers require.
It gives you confidence when reselling or upgrading, since many retailers require certification as part of their programmes.
One detail that often surprises buyers: not all lab-grown diamonds are graded equally. Some retailers use in-house assessments rather than independent laboratories. Others use smaller labs with less consistent methodology. When you are comparing diamonds online across multiple retailers, knowing which laboratory issued the certificate matters as much as the grade itself.
At Marlow's Diamonds, every stone comes certified by IGI or GIA, two of the most trusted independent laboratories in the world. You shop with complete confidence that what is on the certificate is exactly what you are getting.
The Gemological Institute of America was founded in 1931 and is widely credited with creating the standardised language the diamond industry still uses. The 4Cs grading framework, the D-to-Z colour scale, and the international clarity nomenclature all originated with GIA. For decades, a GIA Grading Report was considered the most authoritative document a diamond could carry, and among natural diamonds, that reputation remains fully intact.
GIA began certifying lab-grown diamonds as demand grew, initially using a methodology closely aligned with its natural stone process. That approach has since changed, and those changes are central to understanding the current market.
This is the part of the story that most buyers do not know about, and it explains a great deal about current purchasing trends.
GIA deliberately decided to treat lab-grown and natural diamonds differently in its grading process. The key changes were:
GIA moved to digital-only laboratory-grown diamond reports back in October 2020, while continuing to provide traditional 4Cs grading for those reports. Then, separately, effective October 1, 2025, GIA introduced a new grading framework for lab-grown diamonds, replacing the traditional D-to-Z and clarity nomenclature with two simplified classifications: 'Premium' and 'Standard.
Instead, reports now use just two broad classifications, 'Premium' and 'Standard', rather than precise letter or clarity grades. Diamonds that fall below minimum quality thresholds may not receive a designation.
GIA's new Quality Assessment comes with a simplified printed document showing the Premium or Standard result, and is also accessible digitally via the GIA app or Report Check using the laser-inscribed number on the diamond's girdle. It is not a traditional multi-page grading certificate
The format of a GIA lab-grown report for colourless diamonds now looks and reads differently from a GIA natural diamond report. Fancy coloured lab-grown diamonds are exempt and still receive a full quality assessment with a plotted clarity diagram, issued as a digital-only report
GIA's reasoning is coherent. Lab-grown diamonds and natural diamonds are different products, and the institute's position is that grading them identically would blur a meaningful distinction. The intent is to preserve the significance of its natural diamond grading system.
However, the practical effect on buyers shopping for IGI or GIA certification for lab-grown diamonds has been significant. Buyers accustomed to comparing a precise E colour or VS1 clarity grade now receive a single broad classification, either "Premium" or "Standard" on a GIA lab-grown report, which provides far less detail for comparison purposes.
The International Gemological Institute was founded in Antwerp in 1975 and has built its strongest foothold in precisely the market that has grown most rapidly: lab-grown diamonds. While GIA built its legacy on natural stone grading, IGI invested heavily in lab-grown certification infrastructure as the category expanded, and that investment is visible in its current market position.
For buyers weighing up IGI or GIA certification for lab-grown diamonds, the most relevant distinction is straightforward: IGI continues to use the same traditional grading process it applies to natural diamonds.
What that means in practice:
Colour grades use the standard D-to-Z scale, the same terminology buyers already know
Clarity grades follow the familiar nomenclature from Flawless through to Included
Cut grades are detailed and clearly presented
Physical certificates are still widely available and included as standard by most retailers
That consistency has made IGI the default choice for most retailers operating in the lab-grown space. When you browse certified lab-grown engagement rings at major jewellers today, the certificates you encounter most frequently carry the IGI name. For buyers comparing multiple stones online, the ability to place two IGI-graded stones side by side on the same scale, using the same language, significantly reduces the effort required to make an informed decision.
The table below captures the practical differences buyers need to know when choosing between GIA and IGI certification for a lab-grown diamond.
The single most important row in that table is the second one. IGI uses the same grading process for lab-grown diamonds as it does for natural diamonds. GIA does not. For buyers who want to know exactly where their stone sits on a quality scale they already understand, that distinction drives most purchasing decisions in the lab-grown market today.
Unsure which certification is right for your stone? The team at Marlow's Diamonds has been answering exactly these questions for over 70 years.
Most buyers shopping for a lab-grown diamond in 2026 will find IGI the more practical choice, but the right answer depends on your priorities. Here is how to think through it.
Traditional colour and clarity grades presented in the familiar format
A physical certificate you can store alongside your insurance documents
Straightforward side-by-side comparisons when shopping across multiple retailers online
The same grading methodology used for natural diamonds is applied consistently
The prestige of the most historically recognised name in diamond grading
GIA's evolving approach to distinguishing lab-grown diamonds from natural ones
Simplified quality classification from the institution that built the modern grading system
For most buyers, particularly those purchasing lab-grown engagement rings where the decision involves significant research and online comparison, IGI's consistent and familiar format makes the process cleaner and more confident. That is reflected in where the market has moved: IGI-certified lab-grown diamonds now represent the majority of certified lab-grown stone sales across mainstream retail.
It is also worth keeping one thing firmly in mind, regardless of which laboratory you choose: the certificate is not the diamond. Two stones with identical grades can look meaningfully different depending on how they were cut and how light moves through them. Always ask to see the stone itself, whether in person or through detailed imagery and video, before committing. The grading report tells you where a diamond sits on the scale. Only your eyes can tell you whether it is right.
Both GIA and IGI are respected laboratories. Both employ trained gemologists, both are accepted by insurers and retailers, and both provide genuine independent verification of a diamond's characteristics. Neither should be dismissed.
What has changed is the practical experience of buying a GIA-certified lab-grown diamond. The move away from traditional grading scales and toward a simplified two-tier classification has created a format that some buyers find less familiar and harder to use when comparing stones online. IGI has maintained the consistent process it has always used, and that consistency is what most buyers and retailers are currently choosing.
Understanding the difference means you will not be caught off guard mid-purchase. You will know what each report includes, what it does not include, and which format suits the way you research and buy. That knowledge is what makes the difference between choosing a diamond with confidence and simply hoping the one in the box matches what you were promised.
Marlow's Diamonds has been helping couples across the UK find the right ring since 1951. For over three generations, countless buyers have been guided through these decisions with complete confidence.
