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Can I Trust the Diamond Grading Certificate?

If your diamond comes with a certificate, how do you know it’s legitimate? Learn how to read the “cert” and know where it comes from.

Who knew that choosing a diamond could raise so many questions? The technical information alone can be daunting at first. Add to that the emotional demands of choosing a diamond ring she’ll love, and soon you might feel like your head is spinning.

Several graders at an independent lab evaluate an individual diamond separately, and then reach a consensus to make sure the grade they assign is accurate, consistent and reliable

Not to worry. A diamond certificate, also called a diamond grading report, diamond dossier, diamond quality document or diamond light performance certificate, can help. A diamond certificate contains most of the important information you should know about a finished diamond, including:

  • The 4Cs of diamond quality: the color, clarity, cut and carat weight of a specific diamond viewed under 10x magnification
  • A diamond’s characteristics: proportions, finish, treatments and more
  • Light performance, measuring the bright white light (brilliance), bright color light (fire) and scintillation (sparkle) of a diamond

Some reports include a diagram of the diamond showing its inclusions, which are naturally occurring foreign materials in almost all diamonds that can affect the way light travels through the diamond. Flawless diamonds have no visible inclusions or blemishes under 10x magnification, but they are very expensive and exceptionally rare, representing less than 1% of all finished diamonds.

Check out the diamond certificate before purchasing a diamond engagement ring so you can make a more informed decision. File it with your important papers afterward, and you’ll have easy access anytime you want it. Because no two diamonds are exactly alike, a diamond certificate can even serve as identification in the event of loss or theft.

But can you trust the diamond certificate to be accurate and unbiased? To answer this question, you have to consider the source.

Independent laboratories

You can consider a diamond certificate issued by an independent gemological laboratory reliable because:

  • These laboratories don’t sell diamonds and have no connection to diamond mines, dealers or retailers, so they have no vested interest in the grade they give a diamond.
  • These labs depend on repeat business so they have to maintain a reputation for accuracy and integrity.
  • They use diamond graders and gemologists who undergo intensive training and have passed tests assessing their ability to correctly grade diamonds. 
  • The grade is based on a scientific reading of the diamond’s characteristics using specialized equipment designed just for grading diamonds.
  • Several graders evaluate an individual diamond separately. Because no two diamonds are exactly alike, the graders reach a consensus to make sure the grade they assign is accurate, consistent and reliable.
  • Each diamond certificate is marked with a unique number that matches the exact diamond it describes.
  • Some grading labs offer optional services, including microscopically inscribing the diamond certificate number on the edge (or “girdle”) of the diamond as a security feature.

Back in the lab

Diamond certificates are issued by these well-known independent gemological laboratories:

Gemological Institute of America: 

​GIA pioneered diamond grading in the 1940s, creating a consistent way to describe a diamond in a common language. Today, GIA grading certificates are considered the hallmark of integrity in the diamond world. The private laboratory issues two types of reports. The GIA Diamond Grading Report provides scientifically determined information on shape, clarity, color, cut, carat weight, proportions, finish and treatments. It also includes a diagram of the diamond showing any inclusions that affect clarity. The GIA Diamond Dossier® is a more concise version of the full report and is available for loose diamonds between 0.15 and 1.99 carats. GIA also will laser-inscribe an identification number on the diamond’s girdle that is visible under 10x magnification. The number matches the one on your grading certificate and serves as positive identification that it’s your diamond.

International Gemological Institute:

IGI is an independent grading and appraisal organization with centers in New York City and Los Angeles as well as in Antwerp, Bangkok, Mumbai, Tokyo, Dubai and Toronto. Several gemologists analyze each diamond and produce an accurate description of its characteristics, such as color, clarity, carat weight and the quality of its cut. The information is stored in IGI’s computer database so you may request an update of your report if the need arises. IGI also offers colored gemstone certificates, educational courses and laser inscription services.

Gemological Science International:

GSI is an independent gemological laboratory based in the heart of New York City’s Diamond District with additional offices in diamond centers around the world. GSI offers gemstone identification, grading and appraisal services exclusively to the fine jewelry industry. The lab’s business model is built on integrity, innovation, professional service, and shared research and education.

GemEx Systems:

GemEx is an independent laboratory that focuses on light performance, or the movement of light through the diamond. Trained professionals use the GemEx BrillianceScope® Analyzer to measure a diamond’s white light (brilliance), color light (fire) and scintillation (sparkle). These measurements are then compared with those of other diamonds of the same shape (the highest and lowest amount of white light, color light and scintillation possible for each shape was set by measuring thousands of diamonds). The GemEx Light Performance Report illustrates the measurements for your diamond in a three-bar graph. The report also shows images of your diamond under five different lighting views. Superior performance in any of the three light categories yields a beautiful diamond.

American Gem Society:

AGS Laboratories developed the AGS Performance-Based Cut Grading System. The key to the system is tracing light as it travels through the diamond. That’s what determines whether a diamond looks bright and lively or dull and mediocre. The lab offers several levels of grading reports. The most popular is the Diamond Quality® Document. It shows cut (if available), color, clarity and carat weight accompanied by a profile showing that individual diamond’s measurements along with a custom plot with the actual facet arrangement and inscription details.

Some jewelry stores have their own in-house appraisers. These stores can have as much integrity as the labs, but the evaluation they provide won’t be independent.

If you find a diamond at one of these stores and have concerns about the grading report, simply ask the jeweler to send it to an independent lab for a second opinion. However, if you’re offered a grading certificate by a laboratory that doesn’t have a website, business address and telephone number where you can check references, move on. 

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