Buying a Round Cut Lab Diamond

Understanding the Cut: Why It Matters Most

Cut quality is the most important factor in a round cut lab diamond’s beauty. Unlike color and clarity, which can be subjective, a well-cut diamond will always maximize brilliance, fire, and sparkle.

Super-Ideal and Ideal Cuts: What to Look For

Round diamonds are graded for cut quality, with the best options falling into these categories:

• Super-Ideal Cut – The highest level of precision, maximizing light performance and optical symmetry. These diamonds often receive Hearts & Arrows designation.
• Excellent Cut – A top-tier cut grade, offering outstanding brilliance and fire. While not as precisely crafted as a super-ideal cut, it still delivers exceptional light performance.
• Ideal Cut – A high-performing cut with excellent brilliance and fire, though it may lack the extreme precision of a super-ideal or excellent cut.
• Very Good Cut – Still a decent choice, but may not reflect as much light or appear as lively as ideal or excellent cut diamonds.

To ensure the best brilliance, always choose an Ideal, Super-Ideal or Excellent Cut for a round lab diamond.

This round diamond has poor proportions, resulting in noticeable light leakage and diminished sparkle. A well-cut diamond should have optimal symmetry and precision to maximize brilliance and fire.

The Importance of Proportions and Symmetry

The ideal proportions for a round cut lab diamond ensure that light enters and reflects optimally:

• Table Size: 53%–58%
• Depth: 59%–62.5%
• Crown Angle: 34°–35°
• Pavilion Angle: 40.5°–41°
• Girdle Thickness: T-M-ST

Hearts & Arrows Diamonds: What They Mean

Hearts & Arrows (H&A) diamonds are super-ideal cut diamonds that exhibit perfect symmetry when viewed under magnification. This pattern is a sign of optimal facet alignment, leading to superior brilliance and fire.

Certification and Cut Grading

• GCAL 8X Cut Grade – One of the most advanced cut evaluations available.
• GIA Excellent Cut – A strong choice, though GIA does not measure light performance.
• AGS Ideal Cut (Now part of GIA) – Previously the most precise cut grading system, now merged with GIA.

Cut is the most critical factor in a round lab diamond—even a high-color and clarity diamond will appear dull if it has a poor cut.

Color Considerations for Round Lab Diamonds

While cut determines sparkle, color impacts how white or tinted a diamond appears. Lab-grown round diamonds follow the same color grading scale as natural diamonds, ranging from D (colorless) to Z (light yellow/brown).

1. Best Color Range for Round Lab Diamonds

For the best balance of value and appearance, consider the following:
✔ D–F (Colorless) – Completely white, but premium-priced.
✔ G–H (Near-Colorless) – White in most lighting, offering excellent value.
✔ I–J (Slightly Tinted) – A subtle warmth may be visible, best for yellow or rose gold settings.

H color is often the sweet spot, appearing white in most settings while being more affordable than D–F color diamonds.

2. How Growth Method Affects Color

Lab diamonds are created using either CVD (Chemical Vapor Deposition) or HPHT (High-Pressure High-Temperature) methods, and each affects color slightly differently:

• CVD Lab Diamonds – Sometimes develop brownish or gray undertones, but these can be treated to appear whiter.
• HPHT Lab Diamonds – Typically have a purer white color, making them a preferred option for D–F color diamonds.

3. Fluorescence in Lab Diamonds: Does It Matter?

Unlike natural diamonds, fluorescence in lab diamonds has little impact on appearance. However, in some cases:

• Strong fluorescence may cause a hazy effect, especially in lower-color grades.
• Most high-quality lab diamonds have minimal or no fluorescence, making it a non-issue for most buyers.

For a bright, white appearance, an H+ color grade and a high-quality cut will ensure maximum brilliance.

Clarity: What’s Eye-Clean in a Round Lab Diamond?

Clarity refers to the presence of inclusions and blemishes within a diamond. Since round lab diamonds have a brilliant-cut facet structure, they are better at hiding inclusions than step-cut diamonds like emerald or Asscher cuts.

1. Best Clarity Range for a Round Lab Diamond

✔ VS1–VS2 (Very Slightly Included) – Offers the best balance of high clarity and value, with inclusions that are nearly impossible to see with the naked eye.
✔ SI1 (Slightly Included) – Some stones in this range may be eye-clean, depending on inclusion type and placement. A great option for budget-conscious buyers who review magnified images before purchasing.
✔ VVS1–VVS2 (Very Very Slightly Included) – Inclusions are microscopic and cannot be seen without high-powered magnification. A premium option, but not necessary for an eye-clean diamond.
✔ FL–IF (Flawless and Internally Flawless) – Completely free of internal inclusions, but not worth the premium cost for most buyers.

VS1 or VS2 clarity is the best choice for most buyers, as inclusions in this range are difficult to detect without magnification.

2. Are SI1 Lab Diamonds Eye-Clean?

• SI1 lab diamonds can be eye-clean, but it depends on the location, type, and size of inclusions.
• Black inclusions or ones near the center of the table are more visible than white, feather-like inclusions near the edges.
• High-resolution imaging is essential when buying an SI1 lab diamond—avoid blind purchases without photos or videos.

3. How Lab Diamonds Differ in Clarity from Natural Diamonds

• Lab diamonds tend to have fewer natural inclusions but may show growth-related characteristics, such as strain patterns or metallic inclusions (common in HPHT diamonds).
• CVD diamonds can display silky, wisp-like inclusions, while HPHT diamonds sometimes show minor blue nuance due to boron content.

For the best balance of clarity and value, VS1 or VS2 is ideal, while SI1 can work if carefully reviewed for eye cleanliness.

Carat Weight Considerations: Getting the Right Size

Carat weight affects both price and visual appearance, but it’s important to consider face-up size and proportions rather than just total carat weight.

1. Popular Carat Weights for Round Lab Diamonds

• 1.00ct (6.5mm) – The classic engagement ring size, offering a balance of size and affordability.
• 1.50ct (7.4mm) – A noticeable size upgrade without an extreme jump in cost.
• 2.00ct (8.1mm) – A premium size, making a significant visual impact.
• 3.00ct+ (9.3mm and above) – Statement-size diamonds, though lab-grown options make these more affordable than natural diamonds.

2. Pricing Considerations for Lab-Grown Round Diamonds

• Lab diamond prices are more volatile than natural diamond prices, as lab-grown diamond costs fluctuate with market supply and technology improvements.
• Price jumps occur at 1.00ct, 1.50ct, 2.00ct, and 3.00ct+, so buyers looking for value should consider sizes just under these thresholds (e.g., 0.90ct, 1.40ct, or 1.90ct).

3. Face-Up Size vs. Actual Carat Weight

• A well-cut 1.50ct round diamond (7.4mm) can look larger than a poorly cut 1.75ct diamond with excessive depth.
• Choosing an ideal or super-ideal cut ensures the diamond appears as large as possible for its weight.

Carat weight affects perceived size and pricing, but cut quality has the biggest impact on how large a diamond looks. A well-cut 1.50ct round diamond can look more impressive than a deeper-cut 1.75ct diamond with light leakage.

Certification and Light Performance Imaging

When buying a round cut lab diamond, certification ensures that you’re getting a genuine, high-quality stone with accurate grading. However, not all lab diamond certifications are equal—some labs have stricter grading standards than others.

1. Best Certifications for Round Lab Diamonds

✔ GIA (Gemological Institute of America) – A trusted lab for both natural and lab-grown diamonds, known for strict grading in color and clarity. However, GIA’s lab-grown reports do not include a cut grade, making it necessary to assess cut quality separately.
✔ IGI (International Gemological Institute) – One of the most widely used labs for lab-grown diamonds, offering cut grades along with standard 4Cs grading.
✔ GCAL (Gem Certification & Assurance Lab) – Provides the most detailed cut analysis, including the 8X Cut Grade and light performance data, making it ideal for buyers focused on precision cutting.

2. Why Light Performance Imaging Matters

Even with a high-grade certification, lab diamonds should ideally come with light performance images to verify brilliance, fire, and symmetry. The most useful images include:

• Ideal Scope – Shows if the diamond is leaking light or reflecting light optimally.
• ASET (Angular Spectrum Evaluation Tool) – Measures light return, contrast, and optical efficiency.
• Hearts & Arrows Imaging – Confirms precision-cut diamonds with symmetrical facet alignment.

3. Where to Find Lab Diamonds with Light Performance Imaging

• Whiteflash – Offers detailed light performance reports for precision-cut lab diamonds.
• Brilliant Earth & James Allen – Provide high-resolution videos for easy comparison but their in house diamonds come with some light performance.

For the best quality round lab diamonds, buyers should prioritize certified stones from reputable labs and choose vendors that offer Ideal Scope, ASET, and Hearts & Arrows imaging to confirm superior cut quality.

Best Places to Buy a Round Cut Lab Diamond

Choosing a reputable vendor is just as important as selecting the right diamond. The best retailers provide detailed imaging, strong return policies, and high-quality certification.

1. Top Retailers for High-Quality Round Lab Diamonds

✔ Whiteflash – Specializes in precision-cut lab diamonds with full light performance imaging, ideal for buyers prioritizing cut quality and brilliance.
✔ Brilliant Earth – Offers a wide selection of ethical lab-grown diamonds with high-resolution imaging and customization options.
✔ James Allen – Provides 360° HD videos of every diamond, making it easy to compare clarity and brilliance.
✔ Blue Nile – One of the largest online diamond retailers, with GIA and IGI-certified lab diamonds and detailed imaging.

2. Why Imaging and Certification Matter More Than Price

• Some vendors offer lower prices but lack proper imaging and cut data—avoid purchasing lab diamonds blindly without Ideal Scope or ASET images.
• The best value comes from choosing a well-cut, properly certified round lab diamond with verified light performance data rather than focusing solely on carat weight or discounts.

Key Takeaways for Buying a Round Cut Lab Diamond

✔ Prioritize Ideal or Super-Ideal Cut diamonds for maximum brilliance.
✔ Look for GIA, IGI, or GCAL certification to ensure grading accuracy.
✔ Choose a vendor with light performance imaging to verify cut quality.
✔ Balance color and clarity for value—H color and VS2 clarity are ideal choices.