How to Read a Lab-Grown Diamond Grading Report
A grading report is the closest thing a diamond has to a biography. It records what the stone is, how it was made, how it was cut, and how it measures up against a recognized grading scale. For lab-grown diamonds, the report also answers a question that matters more than most buyers realize: has anything been done to the stone since it left the growth chamber?
The challenge is that most reports are dense, full of abbreviations, and designed for professionals as much as consumers. This guide walks through a lab-grown diamond report section by section, explains what each entry tells you about the diamond’s quality, and shows how to use that information to make a confident decision, whether you are choosing a single stone for an engagement ring or sourcing inventory for a jewelry business.
What a Lab-Grown Diamond Grading Report Actually Is
Which Laboratories Grade Lab-Grown Diamonds?
Not every report carries the same weight. The laboratory’s reputation for consistency is what gives the document its meaning, so the first thing to check on any report is who issued it.
| Laboratory | What to Know About Its Lab-Grown Reports |
|---|---|
| IGI (International Gemological Institute) | The most widely used lab for lab-grown diamonds. Grades color, clarity, and cut on the same scales used for natural stones, and states the growth method and treatment status. |
| GIA (Gemological Institute of America) | The best-known name in natural diamond grading. Its laboratory-grown reports use a simplified quality description rather than the full color and clarity scales it applies to natural diamonds, so always check the current report format. |
| AGS (American Gem Society) | Known for its 0 to 10 cut scale, where 0 is Ideal, and for light performance analysis. AGS Ideal reports are associated mainly with natural diamonds and are rarely seen on lab-grown stones. |
IGI certified diamonds dominate the lab-grown market largely because the IGI grading report gives buyers the familiar language of the 4Cs. If you are comparing loose lab grown diamonds side by side, an IGI report lets you weigh color, clarity, and cut grades directly against one another. That brand recognition and consistency is why many consider IGI the gold standard for lab-grown reports, much as GIA is for natural stones.
Be cautious with reports from lesser-known laboratories. Some apply looser standards, which can make a diamond look a grade or two better on paper than it would at a stricter lab. Two diamonds with identical grades from different laboratories are not necessarily equal.
Reading the Report, Section by Section
Report Number, Date, and Laser Inscription
Lab-Grown Disclosure and Growth Method
Shape, Cutting Style, and Measurements
Carat Weight
Color Grade
Every report carries a unique report number, usually near the top. This number is your key to verifying the document. Most reputable labs let you enter it on their website to view a digital copy of the original report.
On most lab-grown diamonds, the report number is also laser inscribed on the diamond’s girdle, the thin outer edge that separates the crown from the pavilion. IGI inscriptions on lab-grown stones typically include an “LG” prefix before the number. The inscription is microscopic, invisible to the naked eye, and has no effect on beauty or durability. A jeweler can view it with a loupe or microscope to confirm that the stone in front of you is the one described in the report.
The date of issue tells you when the diamond was graded. Diamonds do not change, so an older report remains valid as long as the stone has not been recut, damaged, or treated since.
A legitimate lab-grown diamond report states clearly that the stone is laboratory grown. You will usually see this in prominent wording near the top of the report and repeated in the comments.
Many reports also identify the growth process:
CVD (Chemical Vapor Deposition): the diamond is grown layer by layer from a carbon-rich gas inside a vacuum chamber.
HPHT (High Pressure, High Temperature): the diamond is grown under conditions that replicate the intense pressure and heat deep within the earth.
Neither method produces a better diamond by default. Quality depends on how well the growth is controlled and how skillfully the rough is cut. The disclosure simply gives you a complete scientific picture of the stone.
This section describes the diamond’s outline and facet arrangement. “Round brilliant” is the most common entry. Fancy shapes such as oval, cushion, emerald, pear, and radiant are listed with their cutting style, for example “cushion modified brilliant” or “emerald step cut.”
Measurements appear in millimeters. For round brilliant cuts, the format is minimum diameter, maximum diameter, and depth. For fancy shape diamonds, it is length by width by depth.
These numbers are more useful than they first appear. They tell you how large the diamond will actually look face up, which carat weight alone cannot. Two diamonds of identical weight can have noticeably different diameters if one is cut deeper than the other. For fancy shapes, dividing length by width gives the length-to-width ratio, which determines whether an oval looks slender or round, or whether a cushion looks square or rectangular.
Carat weight is recorded to two decimal places. One carat equals 0.20 grams.
Weight is the most straightforward entry on the report, but it should not be read in isolation. A one carat diamond that is cut too deep can face up smaller than a well-cut stone of lower weight. Read carat weight alongside measurements to understand the diamond’s true visual size.
On reports that use the standard scale, diamond color is graded from D to Z:
• D to F: colorless
• G to J: near colorless
• K to M: faint color
• N to R: very light color
• S to Z: light yellow or brown
Graders determine color by comparing the diamond against master stones, a set of reference diamonds of known color, under controlled lighting. The stone is viewed face down, which makes subtle tints easier to see than they would be in normal wear.
In practice, the difference between neighboring grades is very hard to see with the naked eye, particularly once a diamond is set in finished jewelry. A G or H color diamond typically faces up white in most settings, and yellow gold is forgiving of slightly warmer grades.
Clarity Grade and Clarity Plot
Clarity measures the presence of internal and surface characteristics, known as inclusions and blemishes. Graders assess clarity under 10x magnification using this clarity scale:
| Grade | Meaning |
|---|---|
| FL | Flawless: no inclusions or blemishes visible under 10x magnification |
| IF | Internally Flawless: no inclusions, only minor surface blemishes |
| VVS1, VVS2 | Very Very Slightly Included: extremely difficult to see under 10x |
| VS1, VS2 | Very Slightly Included: minor inclusions, difficult to moderately easy to see under 10x |
| SI1, SI2 | Slightly Included: noticeable under 10x, sometimes visible to the naked eye |
| I1, I2, I3 | Included: obvious inclusions that may affect transparency or durability |
The clarity grade tells you how included a diamond is. The clarity plot tells you where and what. This diagram maps the diamond’s characteristics on an outline of the stone, with red symbols usually indicating internal features and green indicating surface characteristics. A key beside the plot explains each symbol.
The plot deserves real attention. A single small crystal near the edge of the stone may be easily hidden by a prong, while an inclusion directly under the table is far more noticeable. Two diamonds with the same clarity grade can look quite different in person because of where their inclusions sit.
Lab-grown diamonds have their own characteristic inclusions. CVD stones may show small dark graphite-like points, while HPHT stones can contain metallic inclusions from the growth environment. These are recorded the same way as inclusions in natural stones.
Cut Grade, Polish, and Symmetry
Proportions Diagram
Fluorescence
Comments and Post-Growth Treatments
How to Verify a Grading Report
Most reports include a profile diagram showing the diamond’s key angles and percentages:
Table percentage: the width of the top facet relative to the diamond’s overall diameter.
Depth percentage: the diamond’s total depth relative to its diameter.
Crown and pavilion angles: these govern how light enters and reflects within the stone.
Girdle thickness: described on a range from extremely thin to extremely thick. Extremes in either direction can affect durability or hide weight.
Culet: the point at the bottom of the diamond, usually listed as “none” or “pointed” on modern cuts.
For round brilliants, top cut grades tend to fall within a narrow range of table and depth percentages, roughly a table in the low to high 50s and a depth around 59 to 63 percent. These figures are guides rather than rules. The relationship between crown and pavilion angles matters more than any single number, which is why the overall cut grade exists.
Fluorescence describes whether a diamond glows when exposed to ultraviolet light. Fluorescence ratings typically run from None and Faint through Medium and Strong to Very Strong.
In most diamonds, fluorescence has little or no visible effect in everyday lighting. In rare cases, very strong fluorescence can give a hazy appearance. Some HPHT lab-grown diamonds show distinctive fluorescence or phosphorescence reactions, which reflect their growth environment rather than a quality problem. If a stone has strong or very strong fluorescence, view it in daylight before deciding.
The comments section is the part of a lab grown diamond report that buyers most often skip, and it is one of the most important.
Here you will find notes on growth method, inscriptions, and treatments. Some CVD diamonds receive post-growth treatments, most commonly an HPHT process applied after growth to improve color. IGI reports typically state whether the diamond is “as grown” with no indication of post-growth treatment, or whether post-growth treatment is present.
Treatment is permanent and stable in reputable stones. It is not a hidden defect, but it is part of the diamond’s story, and full disclosure is a sign of a trustworthy laboratory and seller. Comments may also note additional clarity characteristics not shown on the plot, or minor details about the grading.
A report is only useful if it genuinely belongs to the diamond in front of you. Verification takes a few minutes:
Check the report online. Enter the report number on the issuing laboratory’s website and confirm that every detail matches the paper or PDF copy.
Match the laser inscription. Ask your jeweler to show you the girdle inscription under magnification and confirm it matches the report number.
Compare measurements. A jeweler can measure the diamond and check that it aligns with the dimensions on the report.
Look for security features. Modern reports often include QR codes, holograms, or other anti-counterfeiting elements.
If anything does not match, ask the seller to request clarification from the laboratory before you proceed.
Lab-Grown vs Natural Diamond Reports: Key Differences
| Feature | Lab-Grown Diamond Report | Natural Diamond Report |
|---|---|---|
| Origin statement | Clearly states laboratory grown | States natural origin |
| Growth method | Often lists CVD or HPHT | Not applicable |
| Treatment disclosure | Notes as grown or post-growth treatment | Notes treatments if detected |
| Laser inscription | Usually includes a lab-grown identifier | Report number only |
| Grading scale | IGI uses the full 4Cs; GIA uses a simplified description | Full 4Cs at major labs |
The grading process is just as rigorous for lab diamonds as it is for natural stones. The differences exist to ensure that the diamond’s origin is never in doubt, which protects buyers and supports industry standards for transparency and ethical sourcing.
A Practical Example: Comparing Two Diamonds
Common Mistakes to Avoid
What This Means for Buyers and Businesses
Frequently Asked Questions
Key Takeaways
• Focusing on color and clarity at the expense of cut. Cut quality has the greatest impact on beauty. Prioritize it.
• Ignoring the clarity plot. The grade is a summary. The plot shows whether an inclusion is likely to be visible.
• Assuming all labs grade the same way. Stick to established gemological laboratories with consistent standards.
• Skipping the comments. Treatment disclosures and growth notes live here.
• Buying without a report at all. A lab grown diamond without independent grading leaves you relying entirely on the seller’s word.
For an individual buyer, the report is your protection and your comparison tool. Use it to narrow your options, then view the diamond itself, because no document fully captures how a stone performs in the light.
For jewelers and retailers, consistent and accurate reports are the foundation of customer trust. Working with an experienced lab diamond supplier means every stone arrives with independent documentation your customers can verify themselves. If you are sourcing wholesale lab grown diamonds, ask about the laboratory used, how treatment is disclosed, and whether stones are inscribed. A reputable lab diamond manufacturer will answer these questions openly, because transparency is what gives a grading report its significant value.
Is an IGI or GIA report better for lab-grown diamonds?
Both are respected laboratories. IGI is more common for lab-grown diamonds and uses the full color, clarity, and cut scales, which makes side-by-side comparison easier. GIA’s laboratory-grown reports use a simplified quality description. The best choice depends on how much grading detail you want.
Does a lab-grown diamond need a grading report?
It is not legally required, but it is strongly recommended. A report from a reputable lab confirms the stone’s identity, characteristics, and treatment status, and supports resale or insurance.
Can a grading report tell me if a diamond is lab grown?
Yes. Gemological laboratories use scientific analysis and specialized equipment to identify laboratory grown diamonds, and the report will state the origin clearly.
What does “as grown” mean on a report?
It means the laboratory found no indication of treatment after the diamond’s growth process was complete.
Are lab-grown diamonds graded more leniently than natural diamonds?
At reputable laboratories, no. Grading lab grown diamonds follows the same standards, tools, and master stones used for natural diamonds.
Can I trust the grades on an online listing?
Only if you can verify them. Always check the report number on the issuing lab’s website before buying.
A lab-grown diamond grading report is your most reliable guide to a stone’s quality, but only if you read beyond the headline grades. Start by confirming who issued the report and verifying the report number. Look for clear disclosure of lab-grown origin, growth method, and any post-growth treatments. Read carat weight alongside measurements, use the clarity plot to understand where inclusions sit, and give cut quality the priority it deserves.
Read this way, a grading report stops being a page of codes and becomes a clear, honest account of the diamond you are about to own or sell.