To be able to evaluate diamonds consistently and make them comparable, the so-called 4 Cs are used, which were introduced by the GIA (Gemological Institute of America).
These 4 Cs describe the most important criteria: Clarity, Color, Cut, and Carat weight.
For the first C, "Clarity," there is a clarity scale that starts with FL (Flawless) and ends with I (Included). Diamonds, like other gemstones, can naturally have inclusions that affect their light reflection and may appear distracting. These inclusions can include crystals/minerals or fractures.
The second C, "Color," describes the diamond's color, which is assessed on a scale from D to Z. D represents colorless, while Z corresponds to a light yellow or brown. Diamonds in the D-F range are considered colorless, G-J as near-colorless, KLM as faint, N-R as very light, and S-Z as light. Completely colorless diamonds are very rare, which is why nearly colorless stones (G-J) are typically used for jewelry. At the other end of the spectrum are so-called "fancy color" diamonds, which fall outside the D-Z color range. In general, blue, green, pink, and red diamonds are among the most expensive.
For the third C, "Cut," which evaluates the symmetry and cut of diamonds, there is a scale ranging from "Excellent" to "Poor." This assessment considers both the symmetrical cut and the proportions of the stone's individual facets.
The better the cut of a diamond, the better it reflects incoming light, resulting in optimal brilliance.
The last of the 4 Cs, "Carat," indicates the weight of a diamond in carats, where 1 ct equals 0.2 grams. A brilliant-cut diamond weighing one carat has a diameter of about 6.4mm.
A carat is divided into 100 points, which is why a 0.5-carat diamond is also referred to as a "50 pointer."