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,…