A diamond certificate is what turns a description into a verifiable fact. Without one, terms like colourless and eye clean are the seller's opinion, and there is no way to compare two stones or two prices meaningfully.
Here is what a report actually is, who issues them, and how to check one.
A report is not an appraisal
These get confused constantly and they are entirely different documents.
A grading report is issued by an independent laboratory. It states the stone's measured characteristics, its 4Cs, dimensions, proportions and any treatments. It contains no valuation. The laboratory has no interest in what the stone sells for.
An appraisal is a valuation, usually produced for insurance, estimating replacement cost at retail. It is not independent grading, and an appraisal figure is not what the stone would fetch if you sold it. Insurance replacement value and resale value are very different numbers, and confusing them leads to unpleasant surprises.
What you want when buying is a grading report from a recognised laboratory.
The main laboratories
GIA, the Gemological Institute of America, developed the 4Cs system now used universally. It has the strongest recognition in natural diamonds and is the usual reference point for the secondary market.
IGI, the International Gemological Institute, is the dominant laboratory for lab grown diamond grading worldwide, applying the same grading methodology. Most certified lab grown stones on the market carry IGI reports.
AGS, the American Gem Society, is well regarded particularly for cut grading.
A practical note. Not all laboratories apply the same standards, and some in store or unbranded certificates grade noticeably more generously. A stone graded two colour grades higher by a lax laboratory looks like a bargain and is not. If a report is from a laboratory you cannot identify, treat the grades with caution.
What is on the report
A full report typically includes the report number and date, shape and cutting style, measurements in millimetres, carat weight, the four grades, polish and symmetry ratings, fluorescence, a plotted diagram showing inclusion positions, and a statement of whether the stone is natural or laboratory grown along with any treatments detected.
The inclusion plot is more useful than most buyers realise. It tells you where the inclusions sit, which determines whether they are visible face up or can be hidden by a setting.
Fluorescence describes how a stone reacts under ultraviolet light. Strong fluorescence can occasionally make a stone appear slightly hazy, though in many cases it has no visible effect and can lower the price of an otherwise good stone.
Laser inscription
Most certified stones carry the report number laser inscribed on the girdle, the thin band around the widest part. It is invisible to the naked eye and readable under magnification.
This is what ties a specific physical stone to a specific report. Without it, a report is a piece of paper that could accompany any similar stone. Lab grown diamonds are typically also inscribed to identify them as laboratory grown.
Verify it yourself
This takes a minute and almost nobody does it.
Every major laboratory publishes an online report verification tool. Enter the report number and the laboratory's own record appears. Check that the grades and measurements match the document you were given, and check the inscription on the stone matches the report number.
Doing this catches both altered documents and reports that simply do not belong to the stone in front of you. Any legitimate seller will expect you to do it.
Frequently asked questions
What is a diamond certificate?
An independent laboratory grading report stating a stone's measured characteristics. It contains no valuation.
What is the difference between a certificate and an appraisal?
A certificate grades the stone independently. An appraisal estimates retail replacement value for insurance and is not independent grading. An appraisal figure is not a resale figure.
Is IGI as good as GIA?
IGI is the dominant laboratory for lab grown diamonds and applies the same grading methodology. GIA carries stronger recognition in the natural diamond secondary market. Both are recognised laboratories.
How do I check a diamond certificate is genuine?
Use the issuing laboratory's online verification tool, enter the report number, and confirm the grades match. Also check the laser inscription on the girdle matches the report number.
Should I buy an uncertified diamond?
Without a report from a recognised laboratory, the stated grades cannot be verified and prices cannot be compared meaningfully.
Our certified stones
The diamonds we hold are independently certified. See the range, read about the 4Cs, or visit the showroom at 124 Peterborough Street, Christchurch.