How to Read a Diamond Grading Report, Line by Line
A grading report looks busy, but it is just a checklist of what a diamond is. Here is what every line means, which parts matter most for how a stone looks, and how to match the paper to the diamond in your hand.
Start with the report number
Near the top of every report is a unique report number. This is the key to everything. On many diamonds, the same number is laser-inscribed on the girdle, the thin edge around the widest part of the stone. A jeweller can show it to you under magnification. If the number on the paper matches the number on the diamond, you know the report belongs to that exact stone.
The 4Cs section
The heart of the report is the 4Cs: cut, colour, clarity, and carat weight, the grading system created by the Gemological Institute of America. Read them in this order:
- Cut: how well the diamond was cut to return light. On a round diamond this is graded from Excellent down to Poor. Cut drives most of the sparkle, so look here first.
- Colour: how colourless the stone is, graded from D (colourless) to Z (light yellow or brown).
- Clarity: how few tiny marks the stone has, from Flawless down to Included.
- Carat: the weight, not the size. Two stones of the same carat can look different sizes depending on how they are cut.
Colour and clarity get the attention, but cut is what makes a diamond come alive. A well-cut stone with a lower colour grade often looks better than a poorly cut stone with a higher one.
Measurements, proportions and finish
Below the 4Cs the report lists exact measurements in millimetres, plus proportions like table size and depth. It also grades polish and symmetry, which describe how cleanly the diamond was finished. For most buyers, Very Good or better on polish and symmetry is plenty.
Fluorescence
Fluorescence is whether the diamond glows under ultraviolet light, usually blue. It is not damage. Faint or medium fluorescence is common and often has no visible effect in daylight. Very strong fluorescence can occasionally make a stone look slightly hazy, so ask to see it in person.
The clarity plot and comments
Many reports include a plot, a small map of the diamond showing where any inclusions sit. Use it to find the stone's natural fingerprint and to confirm you are looking at the right diamond. The comments section notes anything else, such as extra laser inscriptions or clarity treatments. A diamond definition helps here: under the FTC Jewelry Guides, a diamond is pure carbon crystallised in the isometric system, with a hardness of 10.
What the report does not tell you
A report is not a price and not an appraisal. It describes quality, not value. For an insurance value you need a separate appraisal, which we provide. And no report replaces seeing the stone in person, because two diamonds with identical grades can still look different to your eye.
Diamond rings with reports at Vanhess
Every diamond ring here comes with an independent grading report. Bring it in and we will read it with you under magnification.
Single Bezel Diamond Ring - 0.10 ctsFrom $950 CAD
Engagement Ring - C6109XFrom $3,500 CAD
Engagement Ring - C6088XFrom $2,950 CAD
Engagement Ring - C6103XFrom $3,400 CAD
Engagement Ring - C6091XFrom $2,950 CAD
Engagement Ring - K6293RFrom $1,550 CAD
Engagement Ring - B7122RFrom $1,500 CAD
Diamond Ring - B3135RFrom $5,500 CAD
Frequently Asked Questions
Where is the report number on the diamond?
The report number is printed near the top of the grading document, and on many diamonds the exact same number is laser-inscribed onto the girdle, which is the thin edge that runs around the widest part of the stone. You need magnification to read it, so a jeweller will show it to you under a loupe or microscope. Matching the inscription to the paper is the single best way to confirm the report actually belongs to that stone and was not swapped from another diamond. Not every diamond is inscribed, especially older ones, so if you cannot find a number, ask the seller how they verify the report matches. At our Coquitlam studio we will put the stone under magnification with you and check it together.
Which of the 4Cs matters most?
Cut matters most for how a diamond actually looks, because it controls how much light the stone returns to your eye as sparkle. A diamond cut in good proportions bounces light back brightly, while one cut too deep or too shallow leaks light and looks dull, even if it has a high colour and clarity grade. That is why we tell people to read the cut line first and treat it as the foundation of the choice. Colour and clarity still matter, but most buyers get the best value by staying in the middle of those scales where the eye cannot see the difference. If you have to compromise anywhere, protect the cut grade and give a little on the others.
Is fluorescence a bad thing?
Fluorescence is not damage and is usually nothing to worry about. It simply means the diamond glows, most often blue, under ultraviolet light, which is a natural feature of some stones. Faint to medium fluorescence rarely has any visible effect in normal daylight, and in some lower colour grades a touch of blue fluorescence can even make a stone look slightly whiter. The only time to be careful is with very strong fluorescence, which can occasionally give a stone a faint hazy or milky look in bright sun. Because this is uncommon and hard to predict from paper, the simple answer is to view any strongly fluorescent diamond in person before you buy, which we are always happy to arrange.
Does the report tell me what the diamond is worth?
No, a grading report describes quality, not price. It records the 4Cs and the stone's measurements using set standards so you can compare diamonds fairly, but it deliberately does not put a dollar value on the stone. Value depends on the market, the setting, and the day, which is why a separate document called an appraisal exists. An appraisal assigns a monetary value, usually for insurance, and we prepare these in our studio. Think of it this way: the grading report tells you what the diamond is, and the appraisal tells you what it would cost to replace. You often want both, one to choose the stone and one to protect it, and they should never be treated as the same paper.
Can Vanhess read a report with me?
Yes, and we encourage it. Bring the diamond and its grading report to our Coquitlam studio and we will go through the document line by line with you under magnification. We start by matching any laser inscription on the girdle to the report number so you know the paper belongs to that exact stone, then we walk through the 4Cs, the proportions, the fluorescence and the clarity plot so you understand what each part means for how the diamond looks. It does not matter whether you bought the stone from us or somewhere else. Our goal is that you leave understanding your diamond, able to explain it to someone else, and confident that what is on the paper matches what is in your hand.