CVD vs HPHT Diamonds: A Retailer's Guide (2026)

Core Takeaway

• Neither method is inherently superior. For colorless lab-grown diamonds, quality and price are determined by the 4Cs (Color, Clarity, Cut, Carat) and post-growth treatment—not the growth process.

• Both CVD and HPHT stones are real diamonds with identical chemical, physical, and optical properties.

• 1. How HPHT Diamonds Are Grown

  • The Process: Recreates the Earth's upper mantle environment using massive hydraulic presses (cubic, BARS, or belt presses). Extreme pressure (over 870,000 psi / 6 GPa) and high heat (1,300°C–1,600°C) dissolve carbon graphite into a molten metal flux (iron, nickel, cobalt), which recrystallizes onto a diamond seed crystal.

  • Rough Shape: Produces cuboctahedral rough crystals featuring both cubic and octahedral growth faces.

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    Inclusions: Contains tiny metallic flux inclusions (leftover iron, nickel, or cobalt) that appear dark in transmitted light but metallic under reflected light. In rare cases, high metal content gives the stone a weak magnetic reaction.

  • Color Zoning: Growth occurs across multiple directional sectors simultaneously, which can occasionally cause subtle geometric color zoning.

  • Market Fit: Dominates smaller loose stones, accent sizes, and melee diamonds (under 0.50 ct). Over 90% of HPHT diamonds produced today are colorless.

  2. How CVD Diamonds Are Grown

  • The Process: Uses a low-pressure vacuum chamber filled with a carbon-rich gas mixture (typically methane and hydrogen). Microwave plasma breaks down the gas molecules, depositing pure carbon atoms layer-by-layer onto flat diamond seed plates at 900°C–1,200°C.

  • Rough Shape: Produces flat, tabular plates rather than 3D octahedral crystals.

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  • Inclusions: Contains non-metallic graphitic carbon inclusions (dark pinpoints or clouds) rather than metal flux.

  • Color Consistency: Growth occurs in a single direction, producing extremely uniform color distribution without geometric zoning.

  • Market Fit: Dominates 1.00 ct+ goods and large fancy shapes due to lower reactor capital costs and superior scalability into large carat sizes. Most raw CVD crystals grow with a faint brown tint due to structural vacancies.

  3. How to Read HPHT vs. CVD on IGI Certificates

  On an official IGI Laboratory Grown Diamond Report, check the "Comments" section at the bottom to determine origin, diamond type, and treatment status:

  CVD Diamond Certificate Example:

  • Growth Wording: "This Laboratory Grown Diamond was created by Chemical Vapor Deposition (CVD) growth process."

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    Diamond Classification: Listed as Type IIa (chemically pure carbon with no measurable nitrogen, resulting in high optical transparency).

  • Treatment Wording: If the stone was decolorized after growth, the certificate will state "May include post-growth treatment" or note the specific process used.

  HPHT Diamond Certificate Example:

  • Growth Wording: "This Laboratory Grown Diamond was created by High Pressure High Temperature (HPHT) growth process."

  • Diamond Classification: Listed as Type II or Type IIa.

  • "As Grown" Wording: Often states "As Grown—no indication of post-growth treatment." This confirms the diamond achieved its high color grade directly out of the press without secondary heat processing.

  4. Post-Growth Treatment (The Critical Commercial Factor)

  • Why It Happens: Roughly 80% of CVD diamonds undergo post-growth HPHT or LPHT (low pressure high temperature) heat annealing to eliminate brown tints and raise color grades into the D–F range.

  • Permanence: Post-growth heat treatment is 100% permanent, safe, and will never fade, shift, or degrade over time under any lighting or physical conditions.

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  • Disclosure & Value: "As Grown" CVD stones exist, but properly treated CVD stones offer identical brilliance, clarity, and visual appeal. Transparency in reporting is key: disclose treatment status to buyers based on what is stated on the grading report.

  5. Optical & Gemological Differences Under UV Light

  • Phosphorescence (Afterglow): Colorless HPHT diamonds frequently display a brief blue-green phosphorescence (glowing in the dark for a few seconds after short-wave UV light exposure).

  • CVD UV Response: CVD diamonds rarely show visible phosphorescence, though some treated CVD stones may show a weak, short-lived orange or pinkish luminescence.

  • Strain Patterns: Under cross-polarized light, CVD diamonds show distinctive "tatami" or cross-hatched strain patterns caused by layer-by-layer growth, whereas HPHT diamonds show low to no strain.

  6. Pricing & Market Dynamics

  • Value Drivers: Wholesale price lists are based strictly on the final graded 4Cs (Color, Clarity, Cut, Carat)—not on whether the diamond was grown in a press or a plasma chamber. Two 1.50 ct F VS1 Ideal cut round brilliants trade at the same price regardless of growth method.

  • Quality Standard: Manufacturers have largely phased out SI clarity grades from production runs, concentrating supply on high-demand VVS–VS grades with Excellent/Ideal cut standards.

  7. 6 Essential Questions for Your Diamond Supplier

  1. Growth Method: Is the parcel CVD or HPHT?

  2. Treatment Status: Is the stone "As Grown" or post-growth heat treated, and is that noted in the certificate comments?

  3. Lab Verification: Which lab issued the report (IGI, GIA, or HRD), and can the report number be verified online?

  4. Laser Inscription: Is the report number laser-inscribed on the girdle with the appropriate lab prefix (e.g., "LG")?

  5. Chain of Custody: Is full compliance and ethical sourcing documentation available?

  6. Landed Cost: What is the final landed price per carat, including duty, freight, insurance, and local import tariffs?