What Is Diamond Brilliance?

Cut Quality

The quality of the diamond’s cut is the most crucial factor affecting its brilliance. A well-proportioned cut ensures that light entering the diamond is reflected and refracted to maximize sparkle. Poorly cut diamonds, regardless of their carat weight or color, will lack brilliance and appear dull.

• Ideal Cut: An ideal cut diamond has proportions that allow the maximum amount of light to enter the stone, reflect off its internal facets, and return through the top of the diamond. This term refers to a specific grade, while “excellent” or “very good” cuts also exhibit strong brilliance. This precision in cutting is crucial for achieving the highest levels of brilliance. Ideal cut diamonds are often referred to as a specific set of proportions for round brilliance diamonds that aim to maximize light return. It is important to note that not all well-cut diamonds are technically “Ideal Cut” according to the grading standards of institutions like the GIA or AGS. 
• Symmetry: Symmetry refers to the exactness of a diamond’s shape and the arrangement of its facets. Well-symmetrical diamonds reflect light evenly and create a more brilliant appearance. Asymmetrical diamonds, with misaligned facets, can cause light leakage and reduce brilliance.
• Polish: The finish of a diamond’s surface, known as polish, affects how light interacts with the diamond. A well-polished diamond has smooth facets that enhance light reflection, contributing to greater brilliance. Poor polish can create surface marks that scatter light and diminish sparkle.

Proportions

The proportions of a diamond, including the depth, table size, and crown angle, play a significant role in its brilliance. Ideal proportions allow light to travel through the diamond and reflect back to the viewer’s eye efficiently.

1. Depth Percentage: The depth of a diamond, measured by dividing the diamond’s depth by its width, significantly influences brilliance. If a diamond is too deep or too shallow, light escapes through the sides or bottom, reducing sparkle. An optimal depth percentage ensures maximum light reflection and return. The depth and table percentages are most important for round brilliant cuts, and other shapes have different ideal proportions.
2. Table Size: The table is the largest facet of a diamond and affects how light enters and exits the stone. A table that is too large or too small can impact the diamond’s ability to reflect light. Ideally, the table should be proportional to the diamond’s overall size to enhance brilliance.
3. Crown and Pavilion Angles: The angles of the crown (the upper part of the diamond above the girdle) and pavilion (the lower part below the girdle) are critical for light performance. Proper angles ensure that light is refracted within the diamond and reflected back through the crown, contributing to brilliance. Incorrect angles can cause light leakage and reduce sparkle.

Clarity

Clarity refers to the presence of internal or external flaws, known as inclusions and blemishes. While clarity has a lesser impact on brilliance compared to cut quality, significant inclusions can obstruct light passage and reduce the diamond’s sparkle. It is important to understand that in some cases, inclusions like “feathers” can create weak points in a diamond, potentially leading to durability concerns, which is relevant for more active wearers.

• Types of Inclusions: Common inclusions include crystals, feathers, and clouds. Crystals are tiny minerals trapped within the diamond. Feathers are small fractures that can appear white or transparent. Clouds are clusters of tiny inclusions that can create a hazy appearance.
• Impact on Brilliance: While minor inclusions typically do not affect a diamond’s brilliance, larger or more numerous inclusions can obstruct light and diminish sparkle. Diamonds with fewer and smaller inclusions generally have better light performance and higher brilliance.
• Clarity Grades: Diamonds are graded on a clarity scale from Flawless (no inclusions visible under 10x magnification) to Included (inclusions visible to the naked eye). Diamonds with higher clarity grades tend to exhibit greater brilliance because fewer inclusions interfere with light passage.