Shallow Cut vs. Ideal Cut vs. Deep Cut for Gemstones

Why does your 1-carat engagement ring look bigger than mine when they have the same shape and design? In the article How to Make an Engagement Ring Look Bigger, we listed ways in which gemstones of the same carat can look bigger. If the two rings’ chosen gemstone shapes, settings,  designs, metals, and band widths are the same, the primary reason for the size difference is the varying cutting (depth) of the gemstones. Today we will discuss gemstone cutting in detail – shallow cut, ideal cut and deep cut.

To understand these cuts, you first need to understand the principles of reflection and refraction of light in a gemstone.

When light enters a gemstone, it is refracted and reflected. An ideal cut gemstone can return most of the light from the top, creating brilliant sparkle and brightness. If the cutting proportions are improper, light will escape from the sides or bottom, causing the gemstone to appear dull. As shown in the diagram:

The difference between deep cut, shallow cut, and ideal cut is the depth-to-width ratios. Under the same volume, different depth-to-width ratios affect the size of the “face,” resulting in a noticeable difference in appearance. (This is also one reason why “your 1-carat ring looks bigger than mine.”) When the depth-to-width ratios differ, it can lead to variations in cutting angles. The cutting angles of the gemstone (the angles of the crown and pavilion) significantly influence light reflection and refraction, which further affects the optical effects of the gemstone. Next, we will elaborate on the characteristics, pros, and cons of shallow cut, ideal cut, and deep cut.

What is Ideal Cut?

Ideal Cut refers to a gemstone cutting ratio that perfectly meets optical and aesthetic standards. Ideal cut gemstones perform best in light refraction and reflection, maximizing light reflection to produce brilliant fire and brightness. (Especially effective for diamonds and moissanite with high refractive index and high dispersion values.) The following section details how to determine if a gemstone is a standard cut or not.

Pros & Cons of Ideal Cut

Pros:

• Best Optics: Ideal cut gemstones can reflect nearly all incoming light through precise internal reflection paths, creating the most dazzling visual effect. This makes ideal cut gemstones appear more brilliant than other cutting with the same carat weight.
• Best Fire and Brilliance: This cutting fully considers the optical properties of the gemstone, achieving optimal brilliance and fire. This is one of the key standards for measuring gemstone cutting quality.
• Balanced Proportions: Ideal Cut not only ensures optics, but also balances the diameter and depth of the gemstone, making it visually more appealing.

Cons:

• High Cost: The craftsmanship required for ideal cuts is very high, necessitating the removal of more material during the rough stone-cutting process to achieve perfect proportions. This means cutters sacrifice some weight to ensure the best optical performance, resulting in higher prices for ideal cut gemstones.
• Cutting Complexity: Achieving an ideal cut requires experienced craftsmen and precise equipment. Even slight errors can significantly reduce optical performance. Therefore, the production process for ideal cut gemstones is relatively complex and time-consuming.

What is Deep Cut?

Deep cut refers to gemstones that have a larger cutting depth, usually exceeding the proportions of an ideal cut. The gemstone’s height is relatively high, while its diameter appears smaller. Gemstones with this cutting often look smaller than they actually are because their volume extends more vertically.

Pros & Cons of Deep Cut

Pros:

• Thicker and More Durable: Deep cut gemstones extend more in the vertical direction, making them thicker and less likely to break upon impact. (A 1 mm thick piece of glass is more likely to shatter upon impact than a 2 mm thick piece.)
• The Color Is More Intense: The longer light path in deep cut gemstones allows light to stay longer inside, enhancing the gemstone’s color depth and making it more intense. This is particularly noticeable in colored gemstones.

Cons:

• Poor Optical Performance: Deep cut gemstones do not effectively reflect light from the gemstone’s surface; light is mainly concentrated at the bottom. This results in reduced fire (the flashing effect of light) and brightness.
• Visual Size Smaller: Although deep cut gemstones have a strong sense of weight, their diameter appears relatively small from the front, making them look smaller than their actual carat weight.

What is Shallow Cut?

Shallow cut refers to gemstones that have a lower height, making them excessively shallow compared to the ideal cut proportions. Gemstones with this cutting style usually look bigger because they present a larger area on the horizontal plane (i.e., from the front view). However, due to insufficient depth, their optical performance is often unsatisfactory.

Pros & Cons of Shallow Cut

Pros:

• Visual Look Bigger: Shallow cut gemstones look bigger visually because their diameter is typically wider than that of ideal cut and deep cut gemstones. This is appealing to consumers on a budget who want the visual effect of a “larger gemstone.”
• Better for Specific Designs: Shallow cut gemstones may be a deliberate choice in certain jewelry designs, especially when the design emphasizes a flat profile or aims for the gemstone to cover more area.

Cons:

• Light Leakage: Due to insufficient depth, light entering the gemstone cannot fully reflect inside, often escaping directly from the bottom. This makes the brightness and fire effect of the gemstone appear dull.
• Poor Color Performance: Shallow cut gemstones may not adequately showcase the gemstone’s color, especially in colored gemstones, where the shorter light path fails to reveal the depth and saturation of the color.

Which One Is Right for You?

Whether it’s deep cut, shallow cut, or ideal cut, each cutting style has its unique pros and cons. If your budget allows, an ideal cut is undoubtedly the best choice, as it represents the highest standard in gemstone cutting and can maximize the gemstone’s brilliance and fire. If your budget is limited, you can consider deep cut or shallow cut. Prioritize the gemstone’s durability and color depth, choose deep cut. Aiming for a visually “larger” design, go for shallow cut.

How to Determine if a Gemstone is Ideal Cut?

Determining whether a gemstone qualifies as ideal cut mainly relies on specific cutting proportions, angles, and the geometric relationships of facets, which dictate the gemstone’s optical performance, fire, and brilliance.

1. Cutting Proportions

The cutting proportions of a gemstone directly determine its optical effects and overall aesthetic, making it one of the key factors affecting gemstone quality. If the cutting proportions are too large or too small, light cannot be adequately reflected, which impacts the gemstone’s optical performance. The cutting proportions primarily consider the following parameters:

• Table Size: The ratio of the size of the gemstone’s top flat surface to its diameter.
• Crown Height: The ratio of the height of the gemstone’s upper half to its overall height.
• Pavilion Depth: The ratio of the height of the gemstone’s lower part to its overall height.
• Girdle Thickness: The ratio of the thickness of the gemstone’s widest part to its overall height.
• Length-to-width ratio: the ratio of the gemstone’s length to its width as viewed from the top.

2. Cutting Angles

If the angles deviate from the ideal range, light may escape from the bottom or sides of the gemstone, resulting in reduced brightness and fire. This mainly involves the following parameters:

• Crown Angle: The angle between the crown and girdle.
• Pavilion Angle: The angle between the pavilion and girdle.

3. Cutting Symmetry

Symmetry measures the consistency of gemstone cutting. A standard cut gemstone should be perfectly symmetrical in all directions; otherwise, light cannot be evenly distributed and reflected. Ideal cut gemstones should exhibit good symmetry in the following aspects:

• Symmetry of Crown and Pavilion: The facets of the upper and lower parts should align on the same plane without any tilting or unevenness.
• Centered Table: The table should be centered on the gemstone rather than leaning toward one side.
• Alignment of Pavilion Tip: The tip of the pavilion (the pointed bottom of the gemstone) should be positioned at the center of the gemstone.

4. Polish Quality

Polishing refers to how smooth and even the surface of the gemstone is after cutting. A well-polished gemstone will have a high luster, allowing light to freely reflect off the surface without any unnecessary scattering. Poorly polished gemstones may have tiny scratches or uneven surfaces, affecting light transmission. Polishing is typically graded as follows:

• Excellent: Very high polishing quality with a smooth, flawless surface.
• Very Good: Minor imperfections present, but they do not affect the visual effect.
• Good: Average polishing quality, possibly with slight surface flaws. The higher the polishing grade, the better the light reflection on the gemstone’s surface, making it appear brighter.

5. Number of Facets

The number of facets on a gemstone can affect its optical performance. Each cutting shape has a different standard number of facets. An appropriate number is considered optimal for maximizing light reflection paths, enhancing brightness and fire. Insufficient facets may prevent adequate light reflection, making the gemstone appear dull, while excessive facets might lead to light dispersion, reducing the gemstone’s brilliance.

Ideal Cutting Standards for Different Cuts

Although the GIA only provides cutting ratings for round cuts, the concept of “ideal cut” still exists for other shapes in the jewelry industry. (For instance, AGS sometimes offers more cutting ratings for certain cutting shapes.) It is worth noting that the requirements for polishing and symmetry are similar across all cutting types; the main differences lie in the number of facets, cutting proportions, and angles. Below are the cutting standards for 8 common gemstone cuts, which can achieve optimal optical effects.

1. Round Cut

• Table Size: 53% – 57%
• Crown Height: 14% – 16%
• Pavilion Depth: 43% – 44%
• Girdle Thickness: 2.5% – 3.5%
• Length-to-width Ratio: 1
• Crown Angle: 34° – 35°
• Pavilion Angle: 40.6° – 41°
• Standard Number of Facets: 57 or 58 facets (including the bottom point)

2. Princess Cut

• Table Size: 68% – 75%
• Crown Height: 10% – 15%
• Pavilion Height: 43% – 48%
• Girdle Thickness: 2% – 4%
• Length-to-width Ratio: 1
• Crown Angle: 30° – 35°
• Pavilion Angle: 39° – 41°
• Standard Number of Facets: Typically 50 to 58 facets, depending on the specific cutting design

3. Oval Cut

• Table Size: 53% – 63%
• Crown Height: 12% – 16%
• Pavilion Height: 42% – 46%
• Girdle Thickness: 2% – 4%
• Length-to-width Ratio: 1.35 – 1.5
• Crown Angle: 32° – 36°
• Pavilion Angle: 40° – 42°
• Standard Number of Facets: Typically 56 or 57 facets (similar to round brilliant cut)

4. Cushion Cut

• Table Size: 60% – 68%
• Crown Height: 11% – 15%
• Pavilion Height: 43% – 48%
• Girdle Thickness: 2% – 4%
• Length-to-width Ratio: 1.00 – 1.05 (Square）1.10 – 1.20（Rectangular）
• Crown Angle: 34° – 36°
• Pavilion Angle: 41° – 43°
• Standard Number of Facets: Typically 58 or 64 facets, varying slightly by specific design

5. Emerald Cut

• Table Size: 61% – 69%
• Crown Height: 11% – 14%
• Pavilion Height: 44% – 48%
• Girdle Thickness: 2% – 4%
• Length-to-width Ratio: 1.30 – 1.50
• Crown Angle: 28° – 34°
• Pavilion Angle: 43° – 45°
• Standard Number of Facets: 50 to 58 facets, as it has fewer facets due to its step cut

6. Marquise Cut

• Table Size: 53% – 63%
• Crown Height: 12% – 15%
• Pavilion Height: 43% – 46%
• Girdle Thickness: 2% – 4%
• Length-to-width Ratio: 1.75 – 2.25
• Crown Angle: 31° – 36°
• Pavilion Angle: 39° – 42°
• Standard Number of Facets: 56 or 58 facets, typically similar to round brilliant cut facets

7. Pear Cut

• Table Size: 52% – 60%
• Crown Height: 12% – 15%
• Pavilion Height: 42% – 46%
• Girdle Thickness: 2% – 4%
• Length-to-width Ratio: 1.45 – 1.75
• Crown Angle: 33° – 35°
• Pavilion Angle: 40° – 42°
• Standard Number of Facets: 56 or 58 facets, similar to round cuts

8. Radiant Cut

• Table Size: 61% – 69%
• Crown Height: 11% – 15%
• Pavilion Height: 44% – 49%
• Girdle Thickness: 2% – 4%
• Length-to-width Ratio: 1.00 – 1.05 (Square）1.10 – 1.20（Rectangular）
• Crown Angle: 30° – 35°
• Pavilion Angle: 41° – 43°
• Standard Number of Facets: 70 facets (the radiant cut is characterized by having more facets than most cutting shapes)