How to Read an IGI Diamond Certificate

Why the Certificate Matters

The certificate is your only independent evidence of what you're buying.

Without it, you're relying on a jeweller's claim about stone quality. With an IGI certificate and the laser-inscribed report number on the stone, you can:

1. Verify the stone matches the certificate (report number on the girdle matches the document)
2. Verify the certificate is authentic (IGI's online report check at igi.org)
3. Compare quotes: two stones quoted at "1ct G/VS1" may have different cut grades, different fluorescence, or different proportions - the certificate shows all of this
4. Confirm the stone is lab-grown (IGI uses a distinct certificate format for lab-grown)

Every Lux Jewels stone comes with an IGI certificate. Before buying from any jeweller, ask for the specific IGI report number so you can verify it independently.

The IGI Report Number

Located at the top of the certificate. This is the most important field.

The laser inscription on the diamond's girdle matches this number. To verify:

1. Note the report number from the certificate
2. Go to igi.org/verify
3. Enter the report number
4. The result should match the certificate exactly

If there's no report number, or the number doesn't match at igi.org, do not buy that stone.

The laser inscription is microscopic - it's typically visible only under 10x magnification. A gemologist or jeweller can confirm the inscription.

Shape and Cutting Style

The first descriptive field after the report number.

Examples: "Round Brilliant," "Oval Modified Brilliant," "Emerald Cut," "Pear Modified Brilliant," "Cushion Modified Brilliant."

What "Modified Brilliant" means: The stone uses a facet pattern that combines elements of the traditional brilliant cut. It's a standard descriptor - almost all non-round shapes are technically "modified brilliant" or have specific named cutting styles.

Measurements

Expressed as minimum diameter x maximum diameter x depth for round stones (e.g., "6.48 x 6.52 x 4.00 mm") or length x width x depth for fancy shapes (e.g., "9.10 x 6.30 x 3.94 mm").

Why this matters:

• The measurements tell you the actual physical size of the stone, which affects how large it appears on the finger
• Two 1-carat ovals with different measurements have different face-up surface areas - one may appear noticeably larger
• For oval, pear, and emerald cuts, the length-to-width ratio can be calculated from the measurements

Carat Weight

Expressed to two decimal places (e.g., 1.02ct). IGI measures to the hundredths place.

Important: This is the weight of the stone only, not the total weight of any setting or band.

A "1.0ct diamond" is any diamond between 1.00ct and 1.09ct (since the next price tier starts at 1.10ct). There can be a meaningful price difference between 0.99ct and 1.00ct due to psychological pricing in the market - a 0.99ct can represent significant savings at identical visual size.

Colour Grade

Graded on the GIA D-to-Z scale (where D is completely colourless and Z is clearly yellow).

Shape and metal affect colour appearance:

• Step cuts (emerald, Asscher) show colour more clearly - G minimum recommended, F safer
• Round brilliant scatters colour - H acceptable in white gold; I-J acceptable in yellow gold
• Rose gold is warm: H-I in rose gold looks like F-G in white gold
• Yellow gold is warm: H-J acceptable; higher colour is wasted in yellow gold

For lab-grown certificates: The scale is the same as natural diamonds. D colour lab-grown is just as colourless as D natural.

Clarity Grade

Graded under 10x magnification. The scale (GIA system):

Eye-clean is the practical threshold - can you see an inclusion without magnification? Most people can't afford FL/IF lab-grown, and they don't need to. VS1-VS2 is the sweet spot for lab-grown at a reasonable price: clean to the eye, clean under 10x.

SI1 can be eye-clean but depends on the specific stone and the placement of the inclusion. SI2 and below: some inclusions will be visible to the naked eye.

Cut Grade (For Round Brilliants Only)

IGI grades the cut of round brilliants: Excellent, Very Good, Good, Fair, Poor.

Cut determines how light enters, reflects, and exits the diamond - it's the single biggest driver of sparkle. An Excellent cut round at G colour will outsparkle a D colour stone with a Good cut.

For non-round shapes (oval, pear, emerald, cushion), there's no official IGI cut grade. Proportions are described in the measurements and depth/table percentages - but cut quality for fancy shapes is a matter of visual assessment, not a graded scale.

Always request Excellent cut for round brilliants. Very Good can be acceptable; Good and below are not recommended.

Polish and Symmetry

Separate grades: Excellent, Very Good, Good, Fair, Poor.

For polished gem-quality diamonds, Very Good or Excellent is standard. These grades describe the surface condition (polish) and the precision of facet placement (symmetry).

Target: Excellent/Excellent or Very Good/Very Good minimum.

Depth and Table Percentages

Proportions expressed as percentages of the diameter:

• Table %: The large flat facet on top (the "table") as a percentage of the diameter. For round brilliants, ideal range is 54-58%.
• Depth %: Total depth from table to culet as a percentage of the diameter. For round brilliants, ideal range is 61-62.5%.

Stones outside these ranges can be "cut to weight" - keeping carat weight rather than maximizing light performance. The cut grade accounts for this in round brilliants, but knowing these numbers helps you evaluate fancy shapes where there's no formal cut grade.

Fluorescence

The diamond's reaction under ultraviolet (UV) light. Graded: None, Faint, Medium, Strong, Very Strong.

For colour grades G and above: fluorescence can sometimes make a D-E stone appear slightly milky under UV-rich sunlight. This is called the "overblue" or "hazy" effect - it's uncommon but worth checking if you're buying a Very Strong fluorescence stone.

For H-I colour diamonds: Medium fluorescence actually helps by making the stone appear whiter to the eye. It can add value at these grades.

Practical advice: For D-E colour, prefer None or Faint fluorescence. For G-H, Medium is fine. For I and below, Medium or Strong fluorescence can be a value buy.

Clarity Plot

The diagram showing the position and type of inclusions and surface features inside the stone.

Plot markings:

• Red symbols = internal clarity characteristics (inclusions)
• Green symbols = surface characteristics (blemishes)
• Common types: crystal (trapped mineral), needle, cloud, feather (fracture), indented natural

The plot is useful for confirming the stone matches the certificate (inclusions are in characteristic positions) and for understanding what specifically affects the clarity grade.

The "Lab-Grown" Notation

IGI lab-grown certificates use a blue certificate design (as opposed to the beige used for natural diamonds). The words "Lab-Grown Diamond" or "Laboratory-Grown Diamond" appear prominently.

The laser inscription on the girdle also typically includes "Lab-Grown" alongside the report number.

Certificate Verification

Before finalizing any purchase:

1. Obtain the IGI report number
2. Go to igi.org, then Report Check (or the specific verification URL on the certificate)
3. Confirm: stone description matches, colour and clarity match, and the certificate is current

A real IGI certificate will verify instantly. If a jeweller hesitates to provide the report number or the verification fails, do not proceed.

I've reviewed hundreds of IGI certificates over the years with clients across Canada - and I still verify every single stone before recommending it. If you're looking at a lab-grown engagement ring and want a second set of eyes on the certificate details, book a free consultation and we'll go through every field together. I founded Lux Jewels in 2007 and have been working exclusively with lab-grown stones since 2015 - reading these certificates is something I do every day.