Reading a Diamond Grading Report

A diamond grading (per GIA's diamond grading standards) report is usually a single folded sheet, and to a first-time buyer it looks like a form with numbers and words they do not recognize. Yet every line on that page is there for a reason, and reading it properly takes about ten minutes. This guide walks through a typical GIA, IGI or HRD report section by section, explaining what each field means, which numbers actually move price, and which phrases should make you pause. By the end, you should be able to open any grading report and tell whether the diamond in front of you is the one on paper-and whether the price asked is reasonable.

The report is the single most important document in a diamond transaction. It is what lets a stranger in another city buy the diamond without seeing it in person. If you cannot read it, you are trusting the seller completely. At HOLYCOME, we send every stone with its report and a one-line summary of the key grades, because we want the buyer to be able to verify what they are getting. Reading the report is not optional; it is the basic due diligence of buying a diamond.

Which reports this guide covers. The major diamond labs-GIA, IGI, HRD, AGS and GCAL-issue grading reports that follow a broadly similar layout. The exact fields vary, but the core data is the same: report number, lab name, date, carat weight, measurements, color grade, clarity grade, cut grade, polish, symmetry, fluorescence, and a clarity plot. Once you can read one lab's report, you can read the others.

This guide focuses on the GIA Diamond Dossier and Full Report, the IGI Grading Report, and the HRD Antwerp report, because those are the three most common in the international trade. AGS reports use a 0-10 cut scale instead of Excellent to Poor, and GCAL reports add a light-performance score, but the rest of the layout is familiar. Colored stone reports (Gübelin, AGL) are a separate topic and are covered elsewhere on this site.

If the report in front of you is from a lab you have never heard of, that itself is a signal. There are dozens of small labs in India, China and Thailand that will grade a diamond however the seller wants. A report from an unrecognized lab is worth less than the paper it is printed on. The first question to ask when you pick up a report is: which lab issued it?

The header: report number, lab, date

The top of the report identifies the lab, the report number, the issue date and the type of report. The report number is the key. It is unique to that diamond, and it is the number you use to verify the report online. Write it down, and compare it to the girdle inscription on the stone. If the two numbers do not match, the stone is not the one described on the paper.

The date tells you when the stone was graded. A report that is ten years old is still valid-the diamond has not changed-but it is worth checking that the lab's report-check tool still recognizes the number. GIA, for example, has a report lookup that goes back decades. If the date is very recent and the number does not verify online, be suspicious.

The type of report matters. A GIA 'Diamond Dossier' is a shorter report for stones under about 1.5 carats and includes a smaller plot; a 'Full Grading Report' includes a larger plot and more detail. An IGI 'Grading Report' is the standard; an IGI 'Laboratory Report' for very small stones is abbreviated. Make sure the report type matches the size and price of the diamond you are buying.

Measurements and proportions

The measurements are listed in millimeters, usually as two diameters for a round brilliant (e.g. 6.40 - 6.43 mm) plus a depth measurement. The two diameters should be very close; a large difference means the stone is not perfectly round, which is a minor but real defect on a round brilliant. On fancy shapes, the measurements are length, width and depth.

Bring a gauge when you buy. A diamond caliper or a Presidium gauge costs almost nothing and lets you confirm the measurements on the spot. If the report says 6.40 mm and your gauge says 6.60 mm, the stone is not the one on the paper. This check is so quick and so reliable that there is no reason to skip it.

The table percentage and depth percentage are the two proportion numbers that matter most. The table is the size of the flat top facet as a percentage of the diameter. For an ideal round, the table is typically 55 to 60 percent. The depth percentage is the height of the stone divided by its diameter; ideal rounds sit around 59 to 62 percent. If the table is 72 percent or the depth is 70 percent, the cut is probably poorly proportioned and the stone will look dull, even if the cut grade on the report says Excellent.

The proportions section is also where you will find the crown angle, pavilion angle, star length and lower-half length. For a casual buyer, the table and depth percentages are enough. For a deeper dive, these numbers are what the AGS cut grade is built on. If the report lists them, they are worth checking against an ideal-cut chart.

Carat weight

The carat weight is the diamond's mass, measured to two decimal places (e.g. 1.02 ct). One carat is 0.2 grams. The weight is one of the four Cs and a major driver of price: a 1.0-carat diamond costs more than twice as much as a 0.5-carat diamond of equal grade, because weight compounds with rarity.

When you hold the diamond, put it on a gauge. The weight on the report should match the scale. A discrepancy of even a few hundredths of a carat is a red flag: either the stone has been swapped, or the report belongs to a different diamond. This is the simplest and most effective verification check there is.

Note that carat weight is total weight, not visual size. A deep-cut 1.0-carat diamond can look smaller on the finger than a well-proportioned 0.9-carat stone, because more of the weight is hidden below the girdle. This is why cut proportions matter: a shallow or deep stone can 'hide' weight, and the report's proportions section is where you catch it.

Color grade

The color grade on a white diamond is measured on the GIA D-to-Z scale. D is colorless at the top; Z is a light yellow at the bottom. The grade is assigned under controlled lighting, comparing the diamond to a set of master stones. The grade is a single letter, and it matters: going from a G to an I on a one-carat diamond can change the price by 15 to 25 percent, even though the difference to the naked eye is subtle.

On the report, the color grade is usually listed prominently. For fancy-color diamonds (yellow, pink, blue), the color grading is a separate system and the report will say 'fancy vivid yellow' or similar. Fancy colors are a different market entirely, and the report will explicitly state that the color is natural or treated.

Practical tip: the color grade is easiest to judge when the diamond is loose and face-down on a white grading sheet. Once it is mounted in a yellow gold setting, the color looks warmer regardless of the grade. Buy the grade you want for the setting you will use. A J color in white gold looks warm; in yellow gold, it can look perfectly fine.

The difference between adjacent color grades is small. To a trained eye under grading lights, a D and an E are distinguishable; to a normal person in a restaurant, they are not. This is why many buyers pick a G or H color: it is near-colorless, looks white in almost any setting, and costs materially less than a D. The color grade is the four C where the biggest savings hide, because the visual difference is subtle while the price difference is not.

Clarity grade and the plot

The clarity grade measures how many inclusions (internal features) and blemishes (surface features) the diamond has, under 10x magnification. The scale runs from FL (flawless) down to I3 (included). The grades in between are IF, VVS1, VVS2, VS1, VS2, SI1, SI2, I1, I2. Most engagement-ring diamonds fall in the VS to SI range, where inclusions are visible under magnification but not to the naked eye.

The clarity plot is the diagram on the report that shows where the inclusions sit. It uses symbols: crystals, feathers, clouds, needles, and so on. The plot is more useful than the grade itself in one way: it shows you whether the inclusions are under the table (visible when the stone is face-up) or off to the side near the girdle (hidden by prongs). An SI1 inclusion near the girdle can be hidden in a setting; an SI1 inclusion under the table face-up will be visible.

When you look at the plot, note the type of inclusion. A feather (a crack) near the girdle is a structural weak point. A cloud that covers a large area can make the stone look milky. A crystal under the table is usually harmless. The grade alone does not tell you this; the plot does.

For a buyer on a budget, the clarity plot is where you find hidden value. An SI1 stone with a tiny crystal hidden under a prong position can look every bit as clean as a VS2 stone, and it costs less. This is the kind of detail a good jeweler will point out, but only if you ask to see the plot. If you only look at the grade, you overpay for cleanliness that the setting will hide anyway.

Cut grade and finish

For round brilliants, GIA assigns a cut grade ranging from Excellent to Poor. AGS uses a numeric scale from 0 (ideal) to 10. The cut grade is the four C that most directly controls how sparkly the stone looks. A high-clarity, high-color diamond with a Fair cut will look dull, and it will cost less than an Excellent-cut stone of the same grades.

For fancy shapes (princess, cushion, oval, pear), GIA does not assign a single cut grade; instead it lists polish and symmetry grades. Those are still important: a 'Very Good' polish and 'Good' symmetry on an oval means the stone will show some waviness along the edges. Look for Excellent polish and symmetry on fancy shapes unless price is the overriding concern.

Practical note: the cut grade is the one four C where you get the most visual improvement per dollar. Going from a Good cut to an Excellent cut is more noticeable than going from an SI1 to a VS2. If you are on a budget, keep color and clarity in the middle of the range and spend on the cut.

This advice holds whether you are buying a natural diamond or a lab-grown one. On a grown diamond, the color and clarity are already high because the material is grown under controlled conditions. The cut is the variable. At HOLYCOME, our grown diamonds are cut to optimized proportions specifically to maximize brilliance, and the cut grade on the report reflects that. If you are comparing two grown stones of the same price, pick the one with the better cut.

It is also worth noting that cut is the only four C that you can see immediately. Color and clarity require a trained eye and a loupe; cut you see across a room. A well-cut diamond catches light and draws the eye. That is the whole point of buying a diamond, and it is why skimping on cut is the most common and the most expensive mistake buyers make.

It is worth understanding why cut matters so much. A diamond's sparkle comes from light entering the top, bouncing off the inner facets, and returning to the eye. If the angles are slightly off, light leaks out the bottom instead of returning to the eye, and the stone looks dull even though it is perfectly transparent. The cut grade is the lab's measure of whether those angles are right. A high-color, high-clarity stone with a poor cut is a disappointment on the finger; a mid-grade stone with an Excellent cut looks stunning.

Fluorescence, polish and symmetry

Fluorescence is a reaction of the diamond to ultraviolet light. The report lists it as None, Faint, Medium, Strong or Very Strong. About a third of diamonds fluoresce to some degree. In most cases, fluorescence is harmless and even slightly desirable on lower-color stones, because it can make a faint yellow diamond look whiter. On very high-color stones (D-F), strong fluorescence can make the stone look slightly oily, though this is debated.

If the report says 'medium blue fluorescence', do not panic. That is a normal feature, not a defect. The market prices fluorescence only slightly: a strong-fluorescence stone of otherwise high grades trades at a small discount, and a faint-fluorescence stone is often priced the same as a none-fluorescence one. Do not pay a premium for a stone just because it has no fluorescence, and do not accept a big discount on a stone just because it does.

Polish and symmetry are graded Excellent, Very Good, Good, Fair or Poor. Polish is how smooth the facets are; symmetry is how well the facets align. Both affect light return. A diamond with Excellent polish and symmetry will reflect light more cleanly than one with Good grades. On an Excellent-cut round, you should expect Excellent or Very Good on both.

Other fields on the report include the measurements already discussed, the girdle thickness, the culet (usually 'none' for modern stones), and any comments such as 'laser drilling' or 'crystal addition'. The comments section is worth reading slowly; it is where treatments and unusual features are disclosed.

On a round brilliant, the report also lists the star facet length and lower-half length percentages. These are detail numbers that cut specialists use to fine-tune the optical performance. For a normal buyer, the cut grade, polish and symmetry are enough. For someone comparing two Excellent-cut stones side by side, the star and lower-half percentages are where the subtle differences show up.

The inscription and security features

Most modern reports note that the diamond carries a girdle laser inscription, and they print the inscription number on the report. Match that number to what you see under the loupe. GIA reports include a hologram, a micro-print line, and a QR code or report-check number. IGI reports include similar security features. If the paper looks flimsy, the hologram does not shift, or the print quality is off, the report may be forged.

The security features are there because forged reports are a real problem. A counterfeit report on a cheap diamond is a known scam, especially in tourist jewelry markets. The best defense is the online verification step: go to the lab's website, enter the report number, and confirm that the returned record matches the stone in your hand.

Take a phone photo of the report number when you buy, and keep it with your records. If the paper is ever lost, the photo and the online record are enough to prove what the stone is. Some buyers also photograph the stone next to the report number, so there is a permanent visual link between the physical diamond and its paperwork.

Comments, footnotes and treatment disclosures

The comments section of a grading report is easy to skip, but it is where the lab discloses anything unusual. A comment might read 'minor crystal feather near girdle', 'laser drill hole', 'HPHT treated', or 'surface-reaching fracture'. Each comment changes the product. A laser drill hole is a treatment that makes a black inclusion invisible; it is accepted but it reduces the stone's value. An HPHT-treated diamond is a real diamond with a modified color, and it costs a fraction of a natural fancy color.

Read the comments slowly and ask the seller about anything you do not understand. A reputable dealer will explain the comment in plain language and tell you how it affects the price. If the seller waves the comment away or says 'it does not matter', that is a warning. Comments exist because they matter, and a buyer who ignores them is the buyer who overpays.

One comment to watch for on larger stones is 'culet: medium' or 'culet: large'. The culet is the tiny facet at the bottom point of the diamond. On modern cuts it is 'none' (a sharp point). A visible culet means the bottom point was slightly flattened, usually on an older stone, and it can show as a small dark spot when the stone is face-up. It is not a defect, but it is a detail to be aware of.

Digital reports vs paper reports. Most major labs now issue digital reports alongside or instead of paper. GIA, IGI and HRD all let you pull up the report on their websites using the report number. The digital report is identical to the paper one, and it is often easier to read because it is on a screen. You do not need the physical paper to verify the grade; the online record is the record.

That said, keep the paper. A printed report is useful when you take the stone to an appraiser or insurer, and it is a tangible part of the piece's provenance. If you lose the paper, you can reprint it from the lab's website, but the original is more collectible. Some labs charge a small fee for a duplicate paper copy.

QR codes on modern reports let you jump straight to the digital record from a phone camera. This is the fastest verification path: scan the QR code, confirm the grades on the screen match the stone in front of you, and you are done. If the QR code does not resolve to the lab's official site, the report may be fake.

What the report does not tell you

For all its detail, the grading report has limits. It does not tell you how beautiful the diamond looks in person, because beauty depends on the combination of cut, proportions and light performance that a single grade cannot fully capture. Two GIA Excellent-cut diamonds can look noticeably different side by side. The report is a baseline, not a verdict on visual appeal.

The report also does not tell you the price. Pricing is set by the wholesale market, and the same grade stone can trade at different prices depending on where it is bought. The report is the common language; the price is the negotiation. Do not expect the lab to opine on whether you are getting a deal.

Finally, the report does not tell you about the setting. A diamond in a bad setting can look smaller, yellower or less brilliant than its grades suggest. The report describes the loose stone; once it is mounted, the setting metal, the prongs and the halo all change the visual result. Buy the stone on its report, then buy the setting on its own merits. If you are comparing two stones side by side, ask to see them loose, not mounted, so the setting does not bias your judgment. For more on the security side, see every section of a GIA diamond report, and for a step-by-step walkthrough, see how to read a diamond certificate.

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Frequently Asked Questions

Is moissanite a good diamond alternative for retail buyers?

Yes for price-sensitive customers who want brilliance and hardness. Moissanite ranks 9.25 on the Mohs scale, holds up to daily wear and costs a fraction of a natural diamond of the same size, so it resells fast in bridal and fashion lines.

What is the minimum order for wholesale moissanite?

MOQ starts at 50 pieces per design for stock items. Custom cuts and private-label settings usually start at 100–300 pieces depending on the mold.

Do you provide certificates with moissanite stones?

Yes. Every parcel ships with GRA or IGI documentation listing carat weight, color grade and cut. We recommend passing the certificate to your end customer for trust.

How long does sample and bulk production take?

Samples ship in 3–5 days. Bulk runs take 15–20 days under 500 pieces, and 25–30 days for custom work.