An Introduction to Gemstone Grading
An Introduction to Gemstone Grading

Professional Gemologist Certification Course

An Introduction to Gemstone Grading

The Diamond Four Cs Standard

Until the 1950s, no standards for gemstone grading existed. When the Gemological Institute of America (GIA) instituted the Four Cs method for grading diamonds, it revolutionized the industry. This method became the standard we still use today. Prior to this, individual dealers set their own standards. One might grade diamonds as A, B, and C, while another would grade them AAA, AA, and A. In this case, the second dealer's A grade equaled the first's C grade. You can imagine the confusion. Standardization was a boon to both the public and professionals.

Colored Gemstone Grading

On the other hand, colored stones still don't have a gemstone grading standard. It's unlikely they will in the near future, too. Too many gems and too many variables just make a simplified system like the diamond method impossible. So, rather than assigning a grade to a gem, gemologists describe its Four “C qualities:” color, clarity, cut, and carat or weight. For example, an amethyst's color could be described as medium purple or very deep purple with clearly visible red flashes. Gemologists would note any inclusions present, the quality of the lapidary or gem cutting work,...


Donald Clark, CSM IMG

The late Donald Clark, CSM founded the International Gem Society in 1998. Donald started in the gem and jewelry industry in 1976. He received his formal gemology training from the Gemological Institute of America (GIA) and the American Society of Gemcutters (ASG). The letters “CSM” after his name stood for Certified Supreme Master Gemcutter, a designation of Wykoff’s ASG which has often been referred to as the doctorate of gem cutting. The American Society of Gemcutters only had 54 people reach this level. Along with dozens of articles for leading trade magazines, Donald authored the book “Modern Faceting, the Easy Way.”


Never Stop Learning

When you join the IGS community, you get trusted diamond & gemstone information when you need it.

Become a Member

Get Gemology Insights

Get started with the International Gem Society’s free guide to gemstone identification. Join our weekly newsletter & get a free copy of the Gem ID Checklist!