How to Read an IGI Certificate and Truly Understand a Diamond's Value – An Expert's Practical Guide for Buyers
Last updated: 14.03.2026
Publication date: 14.03.2026
Author: Marta Kłosowska
An IGI certificate is a document that allows you to accurately understand the quality and value of a diamond. In practice, without a gemological report, the buyer cannot be sure whether the stone is worth PLN 2,000 or PLN 20,000. From my experience, most customers only look at the weight or price, ignoring the parameters that truly determine the quality of a diamond. In this article, I will show you step by step how to read an IGI report and how to use it when buying a diamond.
In this article, you will learn, among other things:
- how the IGI gemological Institute works
- how to interpret each parameter of a diamond report
- what values indicate a good cut
- what mistakes buyers most often make
- how real diamond valuation works
- where to find diamonds at the best price
Table of contents:
- How to check a diamond report number
- What does Description: Laboratory Grown Diamond mean
- How to interpret Shape and Cutting Style – Round Brilliant
- How to read Measurements 5.10–5.12 × 3.11 mm
- What does Carat Weight 0.50 ct mean
- How to understand Color Grade D
- Is Clarity Grade VVS2 necessary
- Why Cut Grade Excellent is crucial
- What does Polish Excellent mean
- How to interpret Symmetry Excellent
- Is Fluorescence None an advantage
- How laser inscription works
- What does the comment As Grown mean
- How the HPHT process works
- What does Type II diamond mean
- How to interpret Table 58%
- Is Crown Angle 32.7° good
- How to read Crown Height 13.5%
- Why Pavilion Angle 41.1° is important
- What does Pavilion Depth 43.5% mean
- How to interpret Total Depth 60.9%
- What does Girdle Medium mean
- Why Culet Pointed is the standard
- Summary and conclusions
How to check a diamond report number
An IGI report number is a unique identifier assigned to a specific diamond. Thanks to it, you can verify the authenticity of the report in the IGI laboratory database and ensure that the stone's parameters match the documentation. Always check the report number before buying a diamond – it is the absolute foundation of purchase security.
From my experience, most customers do not check the report in the IGI database at all.
And that's the first step.
The report number works a bit like a VIN number in a car.
It allows you to check:
authenticity
stone parameters
assessing laboratory
An example of a specific stone from my valuation:
IGI Report: LG773630068
Parameters:
weight 0.50 ct
color D
clarity VVS2
This is very high quality.
The biggest mistake investors make is buying diamonds without a certificate or with reports from little-known laboratories.
What does Description: Laboratory Grown Diamond mean
The description Laboratory Grown Diamond means a diamond grown in a laboratory. Chemically and physically, it is identical to a natural diamond because it has the same crystal structure. The only difference is where the stone originated.
From my experience, interest in lab-grown diamonds is growing in Poland.
The reason is simple.
Price.
Example client situation:
Budget PLN 5000
Options:
natural diamond
0.50 ct
lab-grown diamond
2 ct
The visual difference is enormous.
How to interpret Shape and Cutting Style – Round Brilliant
Round Brilliant is the most popular diamond cut in the world. It is designed to reflect light to the maximum and create a characteristic brilliance effect. This cut has 57 or 58 facets and is standard for engagement rings.
From my experience, about 90% of customers choose this particular cut.
The reason is simple.
Sparkle.
Light enters through the top of the stone and reflects within it.
How to read Measurements 5.10–5.12 × 3.11 mm
Measurements indicate the actual size of the diamond in millimeters. For a round cut, the diameter of the stone and its height are given. This parameter allows you to assess whether the diamond has correct proportions.
From my experience, customers often only look at carats.
And that's a big mistake.
Two diamonds can have the same weight, but different sizes.
What does Carat Weight 0.50 ct mean
Diamond weight is expressed in carats. One carat equals 0.2 grams. However, the weight alone does not determine the value of the stone – color, clarity, and cut quality are also of immense importance.
Customers most often ask:
"How much does a carat of diamond cost?"
The answer is...
it depends.
Example prices:
natural diamond 0.50 ct
PLN 5000–15000
lab-grown diamond 0.50 ct
PLN 1000–3000
How to understand Color Grade D
Color D signifies the highest possible grade on the diamond color scale. The stone is completely colorless and very rare in nature. Such diamonds are the most highly valued in jewelry.
This color is rare because most diamonds contain trace amounts of nitrogen.
It is nitrogen that causes the yellowish tint.
That's why Color D is so highly valued.
Is Clarity Grade VVS2 necessary
VVS2 clarity means very, very slight inclusions not visible to the naked eye. In practice, this is a very high-quality stone, often used in premium diamonds.
However, my experience shows that most customers can easily buy VS1 or VS2.
The visual difference is minimal.
The price can be much lower.
Why Cut Grade Excellent is crucial
Cut Grade determines the quality of a diamond's cut. An Excellent rating means that the stone's proportions allow for maximum light reflection and the highest brilliance. This is one of the most important parameters in a diamond report.
The biggest mistake investors make is ignoring the quality of the cut.
Because even a diamond with ideal color and clarity can look dull if it has a poor cut.
What does Polish Excellent mean
The Polish parameter in a diamond report refers to the quality of the facet surface finish after the cutting process. An Excellent rating means that the facet surfaces are perfectly polished, allowing light to pass freely through the stone and reflect without optical loss. In practice, a well-polished diamond gives greater brilliance and a cleaner visual effect.
From my experience, this parameter is often underestimated by customers, because most people focus on color and clarity.
In practice, however, polish has a real impact on light reflection.
If the facet surfaces are microscopically uneven or scratched, light instead of returning to the observer's eye:
disperses
escapes sideways
the diamond looks less "lively."
Example from practice.
Two diamonds with very similar parameters:
0.70 ct
color F
clarity VS1
The difference?
The first had Polish Excellent, the second Polish Good.
Under magnification, they looked similar, but in normal light, the second stone was noticeably less brilliant.
Therefore, when buying a diamond, I always recommend clients one rule:
Polish minimum Very Good, preferably Excellent.
In investment diamonds, Excellent is the standard.
How to interpret Symmetry Excellent
Symmetry describes how precisely a diamond's facets are arranged relative to each other. An Excellent rating means that all elements of the cut are perfectly symmetrical, allowing for optimal light reflection within the stone.
From my experience, symmetry is one of the most underestimated parameters by first-time diamond buyers.
Why?
Because it's not easy to understand.
And in practice, it looks like this:
if the facets are not perfectly arranged:
light does not reflect evenly
the diamond loses brilliance
the stone looks less "lively."
An example from my valuation for a client from Warsaw.
We compared two diamonds:
0.60 ct
color E
clarity VS1
The difference was only in one parameter:
first: Symmetry Excellent
second: Symmetry Good
At first glance, they looked similar, but under strong light, the first stone produced much more dynamic reflections.
Therefore, in practice, for brilliant-cut diamonds, it is best to stick to the rule:
Symmetry minimum Very Good, preferably Excellent.
Is Fluorescence None an advantage
Fluorescence describes a diamond's reaction to ultraviolet radiation. In an IGI report, this parameter indicates whether the stone glows under UV light. A None rating means no fluorescence, which in most cases is the most desirable variant.
Customers very often ask:
"Is fluorescence a bad thing?"
The answer is:
it depends on the intensity.
Weak fluorescence often doesn't matter.
However, with strong fluorescence, the effect may appear:
milky appearance
slight haziness of the stone.
From my experience, however, in many cases, fluorescence is also a price opportunity.
Example.
Diamond:
1.00 ct
color G
VS2
Price without fluorescence: approximately PLN 22,000
Price with medium fluorescence: approximately PLN 19,000
The visual difference was minimal.
Therefore, sometimes fluorescence can be a way to make a cheaper purchase.
How laser inscription works
Laser inscription means a microscopic laser engraving on the girdle of a diamond. Most often, this is the laboratory report number, which allows the stone to be unambiguously linked to the certificate.
This engraving is so small that:
it cannot be seen with the naked eye
it does not affect the appearance of the diamond
it can only be seen under a microscope.
From my experience, this is a very important element of purchase security.
Why?
Because it allows you to ensure that:
certificate = specific stone.
In practice, it looks like this:
The client buys a diamond with an IGI report.
The jeweler shows the stone under a microscope.
The report number is visible on the girdle.
This means that the diamond and the document are linked.
What does the comment As Grown mean
The annotation As Grown means that the lab-grown diamond has not undergone additional modifications after the growth process. In other words, the stone has retained its natural properties formed during crystal creation.
In the world of lab-grown diamonds, there are various methods to improve color.
Sometimes used:
heat treatment
structure modifications.
The comment As Grown means that this was not done.
From my experience, this is important to many customers because:
increases trust
means a natural growth process.
How the HPHT process works
HPHT (High Pressure High Temperature) is one of two main methods for creating lab-grown diamonds. The process involves recreating the conditions found deep within the earth – very high pressure and temperature.
In practice, it looks like this:
in a special press:
temperature exceeds 1500°C
pressure reaches 6 GPa.
Under these conditions, carbon begins to crystallize into diamond form.
From my experience, HPHT diamonds are often:
very pure
of good color
structurally stable.
Another popular method is CVD, but HPHT has been a known technology since the 1950s.
What Type II diamond means
The Type II designation refers to the chemical structure of the diamond. Type II diamonds contain very little or no nitrogen. This makes them exceptionally optically pure.
This is why many of the world's most colorless diamonds belong to Type II.
In practice, this means:
very high transparency
no tint
excellent optical properties.
How to interpret Table 58%
The table is the flat top surface of the diamond. In the report, its size is given as a percentage of the stone's diameter. A value of 58% indicates very good proportions for a round brilliant cut.
From my experience, the ideal range is:
54–60%
If the table is too large:
the diamond loses its fire.
If too small:
the stone looks darker.
Is Crown Angle 32.7° good?
The crown angle determines the inclination of the diamond's crown. A value of 32.7° falls within a very good range for a brilliant cut.
Typical ideal range:
32–35°
This parameter affects:
the diamond's fire
how light is dispersed.
How to read Crown Height 13.5%
Crown height defines the height of the diamond's crown as a percentage of the stone's diameter. A value of 13.5% is considered very good for a classic brilliant cut.
A too-low crown reduces the diamond's fire.
A too-high crown can worsen the proportions.
Why Pavilion Angle 41.1° is important
Pavilion angle is the angle of inclination of the lower part of the diamond. This parameter has a huge impact on light reflection inside the stone.
The ideal range is approximately:
40.6–41.2°
If the angle is too small or too large, light "escapes" from the stone.
What Pavilion Depth 43.5% means
Pavilion depth refers to the depth of the lower part of the diamond. A value of 43.5% is very typical for well-proportioned stones.
This parameter works in conjunction with the pavilion angle.
How to interpret Total Depth 60.9%
Total depth is the total height of the diamond relative to its diameter. A value of 60.9% is very close to ideal proportions for a round brilliant cut.
Ideal range:
59–62%
What Girdle Medium means
Girdle is the edge of the diamond separating the crown from the pavilion. The term Medium means the optimal thickness of this element.
A too-thin girdle increases the risk of damaging the stone.
A too-thick girdle reduces the optical size of the diamond.
Why Culet Pointed is standard
The culet is a small facet at the very bottom of the diamond. In modern cuts, it usually has a Pointed form, meaning a sharp tip.
In older diamonds, culets are found to be:
small
medium
but currently pointed is the standard.
Summary and conclusions
IGI vs GIA – which diamond certificate is better
The comparison of IGI vs GIA is one of the most frequent questions from customers buying diamonds. Both laboratories are among the most renowned gemological institutes in the world, yet they have a slightly different history, approach to certifying diamonds, and varying recognition in different markets.
From my experience, clients most often ask:
"Is IGI worse than GIA?"
The answer is not as simple as it might seem.
GIA – history and reputation
The Gemological Institute of America (GIA) is the institute that created the 4C's classification system:
carat
color
clarity
cut
It has been operating since the 1930s and for many years was the absolute standard for natural diamonds.
IGI – global leader in certification
The International Gemological Institute (IGI) was founded in 1975 in Antwerp and is currently one of the largest gemological laboratories in the world.
Importantly:
IGI is a global leader in certifying lab-grown diamonds.
Therefore, if you are buying an HPHT or CVD diamond, you will very often see an IGI certificate.
In practice, it looks like this
From my experience, it appears that:
for natural investment diamonds, GIA is often chosen
for jewelry and lab-grown diamonds, IGI is very often used
However, the most important thing is something else.
A certificate from a reputable laboratory is always better than no certificate.
Common mistakes when reading a diamond report
A gemological report contains a vast amount of information, but many people focus only on a few basic parameters. This leads to erroneous purchasing decisions and often overpaying for a diamond.
From my experience, the most common mistakes buyers make are:
Only looking at carats
The biggest mistake investors make is focusing solely on weight.
Two 1.00 ct diamonds can look completely different.
Reason?
Proportions.
Ignoring cut quality
Customers often choose:
color D
clarity VVS
but ignore cut grade.
And it is the cut that determines the brilliance.
Too high clarity
In practice, most people won't see the difference between:
VVS2
VS1
VS2
Under a loupe, yes.
To the naked eye, no.
That's why I often recommend to clients:
VS1 or VS2 – best value for money.
Lack of price comparison
Price differences between sellers can be huge.
From my experience, it can be:
sometimes even 40–60%.
How much do diamonds cost in Poland in 2026?
The price of a diamond depends on many parameters: weight, color, clarity, cut, and whether the stone is natural or lab-grown. Therefore, two diamonds of the same weight can differ in price by several times.
Example prices (Polish market):
natural diamond 0.50 ct
color F
clarity VS1
approx. 5000 – 10000 PLN
lab-grown diamond 0.50 ct
color D
clarity VVS
approx. 1000 – 2000 PLN
natural diamond 1.00 ct
color G
VS2
approx. 15000 – 35000 PLN
Of course, these are approximate values.
From my experience, the best value for money usually comes from the following configuration:
color F–G
clarity VS1–VS2
cut Excellent
Why it's worth buying a diamond from Diament Expert
From my experience, many people buy diamonds in jewelry stores where prices are significantly higher.
The reason is simple.
Intermediaries.
The Diament Expert model works differently.
You buy diamonds directly from a global stone database.
This allows us to offer:
a vast selection of diamonds
certificates from reputable laboratories
prices often lower than in jewelry stores
Importantly:
we guarantee the lowest price in Poland.
If you find an identical diamond cheaper:
we will refund the difference.
FAQ – frequently asked questions about diamond certificates
Is a diamond certificate necessary?
Yes. Without a gemological report, you cannot be sure what you are buying.
Is IGI a reliable laboratory?
Yes. IGI is one of the largest gemological laboratories in the world.
Is a lab-grown diamond real?
Yes. It has an identical crystal structure to a natural diamond.
Is a diamond with fluorescence worse?
Not always. Sometimes it allows you to buy a stone at a lower price.
Is the report number engraved on diamonds?
Often, yes. Laser inscription allows the stone to be linked to the certificate.
Summary – how to truly read a diamond certificate
A diamond certificate is much more than a document. It is a map of the stone's quality that helps you understand its true value. If you can read an IGI report, you can assess in minutes whether a diamond is a good deal or an overpriced offer.
From my experience, the best strategy when buying a diamond is:
checking the report
analyzing cut proportions
comparing prices
choosing a stone with the best quality-to-price ratio
This way, you can buy a diamond that:
will sparkle beautifully
will retain its value
and will truly be worth its price.
Final expert tip – how to use a certificate when buying a diamond
If you've reached the end of this article, you now know what a diamond certificate is and how to read a gemological report. In practice, this means you are able to independently assess a diamond's authenticity, quality, and real value. And in the diamond industry, that's a huge advantage.
From my experience, many people still buy diamonds or brilliants based solely on appearance, especially when it comes to engagement jewelry or stones for rings. Meanwhile, every diamond, whether it's a jewelry stone or an investment stone, should have a certificate confirming its authenticity and quality.
Such a document is issued by an independent gemological laboratory, which analyzes the diamond's parameters according to the 4Cs system. In practice, this means assessing features such as:
carat (carat / ct)
color (hue)
clarity (diamond clarity)
cut
These four elements form the basis of diamond classification and allow each diamond to be compared with other stones available on the market.
In the world of gemstones, there are several well-known laboratories. You will most often encounter:
International Gemological Institute (IGI)
Gemological Institute of America (GIA)
HRD Antwerp (Hoge Raad voor Diamant)
These are the institutions responsible for diamond certification and establishing the most rigorous standard for diamond evaluation. Therefore, diamonds with certificates issued by these organizations are most valued in trade.
Clients often ask me:
"IGI or HRD?"
"Is an IGI certificate better or a GIA certificate?"
In practice, all three institutes are among the world's leaders, and their gemological report confirms the authenticity of the diamond and its quality parameters. Many people believe that GIA often applies the most rigorous evaluation system, which is why diamonds with a GIA certificate are particularly popular among investors. IGI, on the other hand, is very often used for lab-grown diamonds and cultivated diamonds.
It is worth remembering that each certificate contains a unique identification number, i.e., a certificate number assigned to a specific stone. This identification number is very often laser-engraved on the girdle of the diamond, which allows the stone to be linked to the document and its authenticity to be verified in the institute's database.
A good certificate contains a full report, which is a detailed report describing the diamond's parameters:
color and clarity
cut proportions
presence of inclusions
fluorescence
exact dimensions of the stone
This allows the buyer to compare different diamonds with a GIA, IGI or HRD certificate and assess their real value.
From my experience, the best purchasing strategy is to find a stone with very good proportions and reasonable quality parameters. In practice, this often means choosing:
color F or G
clarity VS1 or VS2
cut Excellent
Such a diamond provides an excellent visual effect while maintaining a very good quality-to-value ratio.
It is also worth remembering that today's market includes both natural diamonds and laboratory-grown diamonds. In both cases, the key is the same – the stone should come from an independent laboratory and have a certificate of authenticity.
So, if you are planning to buy a stone for a ring, investment, or collection, always make sure that the diamond has a certificate issued by an international gemological institute such as IGI, GIA, or HRD Antwerp. Only then can you be sure that you are buying a genuine diamond whose authenticity has been confirmed by specialists.
Finally, one practical tip.
In the diamond industry, it is often said:
"First the report, then the diamond."
If the stone has a diamond certificate issued by a reputable laboratory, you know its diamond parameters and can consciously assess its value. This way, you are buying not only a beautiful stone for jewelry but also a product with clearly defined diamond quality.
And that is why certified diamonds remain the standard in the global gemstone trade.