How to read a diamond grading report

A grading report is a lab's written description of one diamond. The FTC says that when you buy a diamond, "some jewelers will give you a grading report from a gemological laboratory." This guide uses GIA's published guide to its own Diamond Grading Report as the worked example, because GIA explains each line. Other labs issue reports too. We name labs as facts only and do not rank them. Women's Diamond Rings is not affiliated with or endorsed by GIA or any other lab.

What does a grading report cover?

GIA says its Diamond Grading Report grades all four Cs, along with a plotted diagram of clarity characteristics and a drawing of the diamond's proportions. GIA says it issues that report "for loose natural diamonds only, weighing 0.15 carats or more." A diamond already set in a ring, or a lab-grown diamond, may come with a different kind of report, so check what the document covers.

What is on each line?

These are the items GIA lists, in our words:

• Date and report number. When the lab examined the stone, and a unique number on file in the lab's database.
• Shape and cutting style. The outline, and the pattern of the facets.
• Measurements. For a round, the smallest and largest diameter and the depth. For a fancy shape, length, width, and depth.
• Carat weight. GIA records weight to two decimal places. One carat is 1/5 of a gram.
• Color grade. On GIA's D to Z scale. GIA says an asterisk next to the grade means a color treatment was detected.
• Clarity grade. From Flawless to Included, judged under 10x magnification.
• Cut grade. Given only for standard round brilliants in the D to Z range, from Excellent to Poor.
• Polish and symmetry. Each graded from Excellent to Poor.
• Fluorescence. How the stone reacts under long-wave ultraviolet light. GIA says it is used for identification.
• Inscriptions and comments. Any text lasered on the girdle, and notes on features not shown elsewhere. GIA says a detected treatment, such as laser drilling, is described in the comments.
• Proportion diagram and plot. A profile of the stone, and a map of its clarity characteristics with a key to the symbols.

How do you check the report matches the diamond?

Start with the number. GIA says a report number can be laser-inscribed on the girdle, the thin edge of the stone. It says the inscription "is not visible to the naked eye, but can be viewed under 10× magnification." A jeweler with a loupe can read it and compare it with the paper.

GIA says you can match an inscribed number to the paper report or look it up in GIA Report Check, its online database. GIA's guide says the QR code on its report verifies the data against the GIA database. Then compare the measurements on the report with the measurements the seller gives for the stone.

What should you check before you buy?

Use this list with any lab's report:

• The report number matches the stone, by inscription or by the seller's paperwork.
• The measurements and shape match the listing.
• The weight is stated in decimals. The FTC Jewelry Guides say a decimal weight "should be accurate to the last decimal place," and a fractional weight needs a notice that it is not exact plus a reasonable weight range.
• The comments line shows any treatment. The FTC says a jeweler should disclose laser treatment.
• The report says whether the diamond is natural or laboratory-grown. The FTC Jewelry Guides say the word "cultured" may describe a lab-created diamond only with a clear disclosure, such as "laboratory-grown," that it is not a mined stone.
• Comparisons use reports from the same lab. GIA says "Some laboratories may use different standards or processes when grading diamonds."

Is a grading report the same as an appraisal?

No. The items GIA lists on its report include no price or value. GIA describes an appraisal as an evaluation of jewelry, made for insurance or estate purposes. It says many insurance companies require one to set a ring's replacement value, so check what your insurer needs.

Sources: FTC Consumer Advice, Buying Gemstones, Diamonds, and Pearls; eCFR, 16 CFR Part 23, Guides for the Jewelry, Precious Metals, and Pewter Industries (FTC Jewelry Guides); GIA, How to Read a GIA Diamond Grading Report (PDF); GIA, Natural Diamond Grading Reports and Services; GIA FAQ, What is a laser inscription and is it important?; GIA 4Cs blog, How to Protect Your Diamond Engagement Ring; GIA 4Cs blog, Nine Things About Diamond Carat Weight You Need to Know.