How to Read a Diamond Certificate

Diamond certificates are a serious challenge for non-experts. They use strange abbreviations, unconventional report formats, and technical language to encrypt their information. However, familiarizing yourself with how to decode diamond certificates will significantly lessen the pain of understanding what diamond reports say and thereby what they are hiding.

One important point first: “diamond certificate” is the term shoppers commonly use, while laboratories such as GIA and IGI generally use terms like “grading report” or “diamond report.” These documents provide an independent assessment of a diamond's characteristics; they are not the same as a jewellery valuation or appraisal.

For those interested in natural diamonds and lab-grown diamonds, it is now time to learn diamond report reading without the help of a gemologist.

Start Here: The 5 Things to Find First

When you receive a diamond report, take a deep breath.

You don't need to understand everything at once.

Find the following at a minimum:

1. Laboratory
When was the diamond graded? GIA? IGI?

2. Report number
How can you check whether the report is genuine?

3. Diamond origin
If your diamond is natural, this should read 'natural.' If the diamond is lab-grown, this section should read 'lab-grown.'

4. The 4Cs
This section includes the diamond's Carat, Colour, Clarity, and Cut.

5. Comments and disclosures
If there is any diamond growth information, treatments, or details that affect the understanding of the diamond, these will be present in this section.

Once you have discovered these, you can continue your diamond report reading.

Read the Report From Top to Bottom

Diamond reports are like records of a diamond's features. Each section answers different kinds of questions.

1. Who Graded the Diamond?

No laboratory report should be ignored. The report is a laboratory’s analysis for that diamond.

GIA reports include report numbers along with a description of the diamond’s characteristics, and IGI reports provide information on the diamond’s origin, shape, measurements, and grading.

This does not mean you need to select a particular laboratory and nothing else. You need to read and understand the report's analysis.

2. What Is the Report Number?

It is an identification number assigned to a report.

For GIA, the number is documented in its global report database. For GIA Report Check, users can enter report information and compare it to GIA’s database.

You can think of it as the report’s identification number.

If a diamond has a laser inscription on its girdle, that inscription may match the report number, providing another way to connect the physical stone to its documentation.

3. Is the Diamond Natural or Lab-Grown?

This matters in today's diamond-buying market.

A report must define the diamond’s origin as documented in the laboratory’s reporting system.

For instance, IGI reports distinguish natural from lab-grown diamonds. IGI also includes a comments section in its lab-grown diamond reports to document the growth method and treatments.

If you're still deciding, here's a look at the differences between Lab-Grown and Natural diamonds in terms of source and processing, cost versus value, and rarity.

Now Look at the 4Cs

The 4Cs are:

Carat Weight · Colour · Clarity · Cut

They describe a diamond's graded characteristics.

Don't think of the 4Cs as 4 separate values. Think of them as 4 interrelated variables that describe the stone.

Carat Weight: How Much Does It Weigh?

Carat refers to weight, not simply size.

Carats measure the weight of a diamond. One Carat is 0.2 grams. GIA reports diamond weights to the hundredth of a carat.

For example:

1.00 ct = one carat

1.50 ct = one and a half carats

A one carat diamond can look a lot smaller than a one and a half carat diamond due to their different shapes and proportions.

That's why you should also look at the measurements.

Measurements: How Big Is It Physically?

Measurements show the diamond's size.

For round diamonds, GIA describes measurements as:

minimum diameter – maximum diameter × depth

For fancy shapes, measurements are generally given as:

length × width × depth.

This can help compare diamonds of similar weights.

The carat weight gives the weight of a diamond. The measurements give the size of a diamond.

Colour: How Much Colour Does It Show?

In the D-to-Z standard GIA colour grading system, colour is assessed with respect to the level of noticeable colour, from D representing the highest colourlessness, to the maximum value.

Not all diamonds of higher colour grades will be preferable.

Colour can be affected by the following:

• Diamond shape
• Cut
• Size
• Setting
• Personal preference

For this reason, you should also consider the other report factors.

Clarity: What Characteristics Are Inside?

Clarity describes the level of inclusions and blemishes.

Among GIA's clarity grades, we find Flawless (FL) at the top and Included (I) at the bottom, creating a descending scale that includes VVS, VS, and SI. At this level, assessment is made at 10x magnification, including the characteristics, size, number, position, and visibility.

A lower clarity grade does not necessarily make a diamond look visibly flawed.

The Clarity Plot: Your Diamond's Map

Some diamond reports contain a clarity plot which outlines the clarity characteristics documented in the diamond.

GIA explains that this plot is a map of the diamond that shows the characteristics, their position, and their nature. It can represent views of the crown and pavilion.

This is not a schematic or drawing intended to illustrate a diamond defect.

It is a technical record used to support the clarity grade and can help identify the stone.

Cut: Don't Confuse It With Shape

This is one of the most common mistakes.

Shape defines the outline of the diamond:

• Round
• Oval
• Pear
• Emerald
• Cushion
• Marquise

Cut describes the facets, proportions, and finish of a diamond and consequently the diamond’s interaction with light.

For round brilliant diamonds in the corresponding range and colors of D to Z, GIA provides an overall Cut grade.

So, a diamond’s shape and cut are not the same.

Look Beyond the 4Cs

The 4Cs are not the only important factors.

Polish

Polish describes the diamond's surface finish after cutting and polishing.

Symmetry

Symmetry describes the precision of a diamond’s outline and facet alignment.

Both affect the diamond's appearance and are included in relevant GIA and IGI reports.