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Diamond cut refers to the way a diamond has been shaped and faceted from its rough, natural form. The cut is a crucial factor that influences a diamond's brilliance, sparkle, and overall beauty. A well-cut diamond reflects light effectively, allowing it to create those dazzling flashes of colour and light. This guide explains what diamond cut really means, why it matters so much, and how to choose a stone that performs beautifully in the real world, not just on paper.
One of the most common misunderstandings in diamond buying is confusing “cut” with “shape”. A diamond’s shape refers to its outline — round, oval, emerald, pear and so on. The cut refers to how well the diamond has been crafted from its rough form into a finished stone.
A diamond cutter must decide how to arrange each facet so that light behaves in a specific way when it enters the stone. When this is done correctly, light travels through the diamond, reflects internally, and exits back through the top. This is what creates brilliance and sparkle.
If the cut is too shallow or too deep, light leaks out of the sides or bottom instead of returning to the eye. The result is a diamond that looks noticeably dull, even if it has excellent colour and clarity. This is why cut is often considered the most important of the 4Cs of diamonds.
Before exploring how cut influences a diamond's sparkle, it's helpful to understand the different parts that make up a polished diamond. Each section plays an important role in the way light enters, reflects and exits the stone, ultimately determining its brilliance and fire. A diamond consists of several key components:
Table: The large, flat facet at the very top of the diamond. This is the primary point where light enters and exits the stone.
Crown: The upper portion of the diamond, located between the table and the girdle. The crown's angles influence how light is dispersed, contributing to the diamond's fire.
Girdle: The narrow outer edge that forms the widest part of the diamond. It separates the crown from the pavilion and is where the diamond is typically secured within a setting.
Pavilion: The lower section of the diamond beneath the girdle. Its angles are critical for reflecting light back through the top of the stone. If the pavilion is too deep or too shallow, light can escape, reducing brilliance.
Culet: The small facet, or point, at the very bottom of the diamond. Modern diamonds often have a very small or virtually invisible culet to maximise light performance.
A diamond is essentially a carefully engineered reflector of light. Its beauty depends entirely on how efficiently it handles that light. When a diamond is well cut, three distinct visual effects come together:
The first is brilliance, which refers to the return of white light. This is what gives a diamond its brightness and “presence” even in low-light environments.
The second is fire, which is the dispersion of light into subtle rainbow colours. This effect becomes visible when the diamond moves under direct lighting and adds a sense of vibrancy.
The third is scintillation, which is the pattern of sparkle and contrast created as the diamond moves. This is what makes a diamond feel dynamic rather than static.
When these three elements are in balance, the diamond appears lively and full of depth. When they are not, the stone can look flat or glassy, regardless of its size or clarity grade. This is why two diamonds with identical certificates can look completely different in person.
Not all diamonds are cut to the same standard. To help buyers understand the quality of a diamond's cut, independent gemmological laboratories assess how well a diamond has been proportioned and finished.
The two laboratories most commonly encountered are the Gemological Institute of America (GIA) and the International Gemological Institute (IGI). Both evaluate a diamond's cut using strict grading criteria, although there are slight differences in terminology.
When grading a diamond's cut, laboratories consider several factors, including its proportions, facet arrangement, symmetry and polish. Together, these determine how effectively the diamond reflects and returns light, which directly influences its brilliance, fire and scintillation.
Diamonds are typically cut using three main styles:
Brilliant Cut:
Brilliant cuts are designed to maximise sparkle and light return. They feature triangular and kite-shaped facets arranged to reflect as much light as possible. Common examples include the round brilliant and princess cuts. Brilliant-cut diamonds typically have 57 or 58 facets.
Step Cut:
Step cuts feature long, rectangular facets arranged in parallel lines, creating a clean, elegant “hall of mirrors” effect. Popular examples include the emerald cut and Asscher cut. Step-cut diamonds usually have 44 to 48 facets.
Mixed Cut:
Mixed cuts combine elements of brilliant and step cuts and aim to capture the best of both. Common examples include the radiant and cushion cuts with facet counts ranging from 58 to over 70 facets.
When selecting a diamond, cut should always be your starting point. It has a greater impact on beauty than carat weight, colour or clarity.
As a general guide, Excellent or Very Good cut grades are recommended for round brilliant diamonds intended for engagement rings or fine jewellery.
Beyond grading, however, it is equally important to observe how the diamond performs in real lighting conditions. Natural daylight, indoor lighting and movement all reveal different aspects of a diamond’s cut quality. A slightly smaller diamond with superior cut will almost always appear more brilliant than a larger stone with weaker proportions.
Many buyers unintentionally prioritise the wrong factors when buying a diamond.
One of the most common mistakes is focusing too heavily on carat size while neglecting cut quality. A larger diamond may seem appealing, but if poorly cut, it will lack brilliance and appear less impressive.
Another mistake is assuming that all Excellent cut diamonds look identical. In reality, proportions vary within the grade, meaning performance can still differ significantly.
Some buyers also overlook shape-specific issues such as bow-ties in oval diamonds or windowing in emerald cuts.
Finally, purchasing a diamond without seeing how it performs in real lighting conditions can lead to disappointment, as certificates alone cannot fully capture visual beauty.
Diamond experts at Regal look beyond the diamond certificate. While GIA and IGI grades provide an excellent benchmark, they don't always reflect how a diamond performs in real life.
Our experienced jewellers carefully assess each diamond for its brilliance, fire and overall light performance, ensuring every stone meets our high standards before it's selected.
Visit our Hatton Garden showroom or book a private consultation to view our hand-selected diamonds side by side. We'll help you understand the subtle differences between each stone, ensuring you choose a diamond that offers exceptional beauty, quality and value.
