Diamond's characteristics can be summarised using the 4 C's: cut, carat, clarity and color.
The cut of a diamond is an important factor in determining its brilliance and fire. The cut should be proportionate and symmetrical, with a balanced combination of depth, table, crown, girdle and pavilion angles. The facets should be well-aligned to allow maximum light refraction and dispersion. The most common diamond cut is the round brilliant, which has 57 or 58 facets.
The carat is a unit of weight used to measure diamonds and other gemstones. One carat is equal to 0.2 grams, and the size of a diamond increases with its carat weight.
Clarity refers to the number, size and type of inclusions and blemishes present in a diamond. Inclusions are internal features, such as cracks, feathers, and foreign crystals, while blemishes are external features, such as scratches and chips. The clarity grade of a diamond is determined by how visible these inclusions are under 10x magnification.
The color of a diamond is graded on a scale from D (colorless) to Z (light yellow or brown). A colorless diamond is the most valuable and desirable, while diamonds with visible yellow or brown tints are less valuable.
The diamond color scale is a standardized grading system created by the Gemological Institute of America (GIA) that assesses the absence of color in a diamond . The scale begins with the letter D, representing colorless , and continues with increasing presence of color to the letter Z. The grades are subdivided in five subcategories: Colorless (D-F), Near Colorless (G-J), Faint (K-M), Very Light (N-R), and Light (S-Z).
Here is a chart of the GIA diamond color scale:
D Colorless E Colorless F Colorless G Near Colorless H Near Colorless I Near Colorless J Near Colorless K Faint L Faint M Faint N Very Light O Very Light P Very Light Q Very Light R Very Light S Light T Light U Light V Light W Light X Light Y Light Z Light
Presence or lack of fluorescence can also affect the desirability and thus the value of a diamond . Fluorescence is a phenomenon in which a diamond emits visible light when exposed to ultraviolet (UV) radiation.
The GIA Diamond Color Scale is a standard used to grade the color of diamonds. It ranges from D (colorless) to Z (light yellow or light brown). This scale is often accompanied by a chart showing the different colors of fluorescent diamonds, which can range from Faint to Very Strong. Fluorescence is caused by the presence of nitrogen in the diamond and can be seen when the diamond is exposed to ultraviolet light. Fluorescent diamonds often appear brighter and whiter in color than non-fluorescent diamonds but can appear milky or hazy at times. The GIA Diamond Color Scale with Fluorescence Chart can be found here: https://www.gia.edu/diamond-fluorescence-chart.
Refraction is the bending of light as it passes through a diamond, resulting in the rainbow of colors seen in the gem. Dispersion, or the separation of white light into its component colors, is also caused by the refraction of light in a diamond.
Facet names and descriptions are important to understand when evaluating the cut of a diamond. The table facet is the flat top-most surface of the diamond, and the crown is the top portion above the girdle. The pavilion is the bottom portion below the girdle, and the culet is a tiny flat facet at the point where the facets meet . The girdle is the widest part of the diamond, and the depth is the distance between the table and the culet.