How Diamonds are Graded: Grading Diamonds
About the 4Cs
Every diamond is unique. Each reflects the story of its arduous journey from deep inside the earth to a cherished object of adornment. Yet all diamonds share certain features that allow us to compare and evaluate them. These features are called the 4Cs and they help us in grading diamonds.
Carat Weight: One carat equals 1/5 of a gram in weight. For diamonds under a carat, each carat is divided into 100 points – similar to pennies in a dollar. 0.75ct. = 75 points, ½ ct. = 50 points
Clarity: The GIA Clarity Scale includes eleven clarity grades ranging from Flawless to I3. Given that diamonds form under tremendous heat and pressure, internal and external characteristics are common. These characteristics help gemologists separate natural diamonds from synthetics and simulants, and identify individual stones.
There are two types of clarity characteristics: inclusions and blemishes – the difference is based on their locations. Inclusions are enclosed within a diamond while blemishes are confined to its surface.
Color: The GIA Color Scale extends from D (colorless) to Z (light yellow or brown). Although many people think of gem quality diamonds as colorless, most diamonds used in jewelry are nearly colorless with tints of yellow or brown. Color grades are determined by comparing each diamond to a master set. Each letter grade represents a range of color and is a measure of how noticeable the color is.
Cut: The GIA Cut Scale ranges from Excellent to Poor. A polished diamond’s beauty lies in its complex relationship with light: how light strikes the surface, how much enters the diamond, and how, and in what form light returns to your eye.
A polished diamond’s proportions affect its light performance, which in turn affects its beauty and overall appeal. Diamonds with good proportions optimize the interaction with light, and have good brilliance, fire, and scintillation.
The Design (weight ratio, durability) and Craftsmanship (polish, symmetry) of a diamond also affect its cut quality, and are considered in determining a diamond’s GIA Cut Grade.
Fluorescence: Many diamonds emit a visible light when exposed to ultraviolet radiation. Although fluorescence is not a factor in determining color or clarity grades, a description of its strength and color is provided on GIA Reports for identification purposes.