CVD vs. HPHT Lab-Grown Diamonds: A Complete Guide to the Two Technologies
Updated: Oct 8
The key difference lies in how carbon reaches the diamond seed. In CVD, carbon-containing gases are broken down, allowing carbon to deposit layer by layer on the seed and form a diamond. HPHT, by contrast, uses extremely high pressure and temperature to dissolve carbon in a metal solvent before it crystallises onto the diamond seed.
Both are established methods for growing lab-grown diamonds, but they differ in their growth environments, potential identifying characteristics, and post-growth treatments. Below, we explain how each method works, then compare the resulting diamonds and the key information to consider when choosing one.
Table of Contents
1. How Do CVD Diamonds Grow?
CVD stands for “Chemical Vapor Deposition.” A small piece of diamond is first placed in the growth chamber as a “seed.” Carbon-containing gases such as methane are then introduced into the chamber at low pressure. Microwaves energize the gases, breaking their molecules apart so that carbon can deposit onto the seed and grow layer by layer, following the existing crystal structure.
The result is a rough diamond that still needs to be cut and polished before becoming the diamond set in a ring. CVD refers to how the diamond is grown, not its colour, clarity, or cut grade.
2. How Do HPHT Diamonds Grow?
HPHT stands for “High Pressure High Temperature.” The growth chamber contains a carbon source, a metal solvent, and a diamond seed. The equipment applies extremely high pressure and temperature, causing the carbon to dissolve in the molten metal and then move toward the cooler diamond seed, where it gradually crystallises into diamond.
HPHT is therefore not simply a matter of “pressing graphite into diamond.” The metal solvent and diamond seed are both important components of the conventional growth process. Once the rough diamond has formed, it must also be cut and polished. This method replicates some of the high-pressure and high-temperature conditions associated with natural diamond formation, but the resulting diamond is still a lab-grown diamond.
3. Key Differences Between CVD and HPHT
Comparison Criteria | CVD | HPHT |
Source of Carbon | Carbon-containing gases such as methane | Carbon sources such as graphite |
Growth Environment | Low-pressure growth chamber; gases are energised | Extremely high pressure and high temperature |
How Carbon Reaches the Diamond Seed | Carbon is released from the gases and deposits onto the surface of the diamond seed | Carbon first dissolves in the metal solvent, then crystallises onto the diamond seed |
After Growth | The rough diamond requires cutting and polishing; some diamonds may undergo post-growth treatment to improve colour | The rough diamond requires cutting and polishing; post-growth treatment may also be applied as needed |
The table above compares growth methods, not the quality ranking of the finished diamonds. Both CVD and HPHT can produce colourless diamonds suitable for jewellery.
4. How Do the Appearance and Quality of the Two Types of Diamonds Differ?
The growth method can influence certain characteristics, but it does not determine the appearance of every diamond. Some CVD diamonds may have a brownish tint and undergo HPHT treatment to improve colour. HPHT diamonds may show a yellow or blue tint depending on elements absorbed during growth, and may sometimes contain metallic inclusions. Modern technology can produce high-colour CVD and HPHT diamonds, so these characteristics do not apply to every stone.
“Which one has more sparkle?” Sparkle depends more on the diamond’s cut, proportions, symmetry and polish than on whether it is CVD or HPHT. When comparing diamonds, colour, clarity and transparency should also be considered. The growth method alone does not determine a diamond’s appearance or quality.
5. What Is the Difference Between HPHT Growth and HPHT Post-Growth Treatment?
“HPHT” can refer to either the growth method or a post-growth treatment. If a report states “CVD growth” and “may have undergone HPHT treatment,” it means the diamond was originally grown layer by layer using CVD and later treated under high pressure and high temperature to improve its colour. It remains a CVD-grown diamond.
Post-growth treatment information helps you understand how the diamond was processed, but it is not an independent measure of quality. When comparing diamonds, consider this information together with the final colour and clarity grades, cut, visible colour and price.
6. Do Diamond Grading Reports State CVD or HPHT?
First, verify the report number and confirm the diamond is identified as “Laboratory-Grown.” Then review the report’s comments or additional information. Some GIA reports specify the growth method, while the more concise Laboratory-Grown Diamond Report – Dossier does not include growth method or post-growth treatment details. IGI reports may also disclose this information. If the method is not stated, do not assume the diamond is CVD or HPHT.
Distinguish between “grown by CVD/HPHT” (growth method) and “post-growth treatment” (treatment after growth). Always refer to the individual diamond’s grading report rather than relying solely on the product description.
7. How Should You Compare Diamonds When Buying?
Start by comparing diamonds with similar budgets, shapes, carat weights and colours. Then review each report for dimensions, clarity, cut, polish, symmetry and comments. Compare videos under consistent lighting, paying attention to face-up brightness, any brown or blue tint, transparency and actual size. If possible, view the diamonds in person before considering quality and price together.
At RAGAZZA, when comparing two round brilliant lab-grown diamonds of similar specifications, we also use our independently developed DAII™ Quality Index to examine differences in proportions and quality beyond the 4Cs. You can compare individual specifications and prices through Choose Your Diamond, then make your choice based on the appearance, light performance and budget that matter to you.
Frequently Asked Questions
Are HPHT diamonds natural diamonds?
No. HPHT diamonds are grown in a laboratory using high pressure and high temperature. Like CVD diamonds, they are lab-grown diamonds. Natural diamonds have a different origin and growth process.
Are CVD diamonds softer or less durable because they are grown at lower pressure?
No. CVD produces diamond crystals, and the lower pressure of the growth chamber does not make them softer. For everyday jewellery, factors such as cutting, setting and proper care should also be considered.
Can a diamond be described as both CVD and HPHT?
Yes. For example, a diamond may be grown using CVD and later undergo HPHT post-growth treatment. The two terms describe different stages—growth and post-growth treatment—so it is important to check the relevant sections of the grading report.
Further Reading: RAGAZZA Lab-Grown Diamond Collection
Sources: GIA Research on Lab-Grown Diamond Growth; GIA Guide to Growth Method Reporting; GIA Dossier Report Information; IGI Lab-Grown Diamond Report Information
Original content by RAGAZZA Diamond. All rights reserved. No unauthorized reproduction or use.
Visit a RAGAZZA DIAMOND showroom by appointment for a one-to-one consultation with our diamond specialists.
Showroom Locations & Appointments Click Here
