GIA sets the benchmark with its diamond color-grading scale, starting at D for colorless and progressing towards Z for light yellow or brown hues. Each letter grade delineates a distinct range of color appearance. Diamonds undergo color grading by comparison with stones of known color under controlled lighting and precise viewing conditions. 

These subtle color differentiations, often invisible to the untrained eye, significantly impact the quality and price of a diamond.

The first three components—brightness, fire, and scintillation—relate to the diamond's appearance, reflecting its total light, color dispersion, and pattern of sparkle. The remaining four factors—weight ratio, durability, polish, and symmetry—pertain to the diamond's design and craftsmanship. Each component is individually assessed within GIA's system, considering its relative importance to the overall cut quality. The resulting cut grades range from Excellent to Poor, representing various proportion sets and face-up appearances. These proportions, including table size, crown angle, and pavilion depth, significantly influence how the diamond interacts with light, shaping its attractiveness to the observer.

Consider a side view of the standard round brilliant diamond, showcasing its main components: the crown, girdle, and pavilion. This cut typically features 57 or 58 facets, with the 58th facet known as the culet, a tiny flat facet at the pavilion's base. At the top lies the table, a large, flat facet. Diamond proportions involve the relationships between table size, crown angle, and pavilion depth, crucial for how the stone interacts with light and its appeal to the viewer.

Similar to how a dollar divides into 100 pennies, a carat divides into 100 points. For instance, a 50-point diamond weighs 0.50 carats. However, two diamonds of equal weight can hold vastly different values based on the other components of the Four C's: clarity, color, and cut. The majority of diamonds utilized in fine jewelry are one carat or smaller. Given that even a fraction of a carat can significantly impact cost, precision is paramount. In the diamond trade, weight is often measured down to the hundred-thousandths of a carat, then rounded to the nearest hundredth of a carat. Diamonds weighing more than one carat are expressed in carats and decimals. For example, a 1.08 carat stone would be stated as "one point zero eight carats," or "one oh eight."