How Are Lab Grown Diamonds Made? HPHT vs CVD Explained Simply

Published: July 24, 2026 Reading Time: 9 min Part 12 of the Zalkari Moissanite and Lab Grown Diamond Series

Lab grown diamonds are made through two processes: High Pressure High Temperature (HPHT), which replicates the conditions under which natural diamonds form in the earth's mantle, and Chemical Vapor Deposition (CVD), which builds diamond crystal atom by atom from a carbon-rich gas. Both produce genuine diamond pure carbon in the diamond cubic crystal structure with Mohs hardness 10 and the same optical properties as natural diamond. The production method is noted on grading reports but does not make one stone better or worse than the other for buyers in most everyday jewelry contexts.

Understanding how lab grown diamonds are made helps buyers evaluate quality claims, read grading reports accurately, and understand why certain visual characteristics appear in lab grown stones that differ from natural diamonds.

Why Growing Diamond in a Lab Is Possible

Diamond is carbon. Carbon is one of the most abundant elements in the universe. The challenge with creating diamond is not obtaining carbon it is arranging carbon atoms into the specific cubic lattice structure that makes diamond what it is.

In nature, carbon becomes diamond when it is subjected to pressures of approximately 725,000 pounds per square inch and temperatures above 1,200 degrees Celsius deep in the earth's mantle, then transported to the surface through volcanic activity over millions to billions of years. The conditions are extreme and the timeline is enormous.

Replicating those conditions or creating alternative conditions that produce the same result is what both HPHT and CVD accomplish. The science has been understood since the 1950s. General Electric produced the first synthetic diamonds in 1954. Producing gem-quality stones suitable for jewelry took additional decades of refinement. By the late 1990s, gem-quality lab grown diamonds were commercially available, and the 2010s brought the production scaling that made today's pricing possible.

HPHT: High Pressure High Temperature

HPHT directly replicates the conditions that create natural diamond. A carbon source typically graphite or a small diamond seed crystal is placed in a growth chamber along with a metal catalyst, usually an iron-nickel alloy. The chamber is compressed to pressures exceeding 1.5 million pounds per square inch and heated above 1,400 degrees Celsius.

Under these conditions, the carbon from the graphite dissolves into the molten metal catalyst and migrates to the diamond seed, where it crystallizes in the diamond cubic structure. The crystal grows outward from the seed over a period of days to weeks depending on the target size.

HPHT growth tends to produce cuboctahedral crystals roughly cubic with some octahedral faces which reflects the geometry of the cubic crystal system. The growth sectors visible in HPHT diamonds under advanced spectroscopy have a characteristic pattern that differs from both natural diamonds and CVD diamonds, allowing gemological laboratories to identify the growth method.

One characteristic of some HPHT diamonds: nitrogen incorporation during growth can produce a slight yellow or brown tint, depending on growth conditions. The finest HPHT production achieves colorless grades by controlling nitrogen carefully, but HPHT diamonds trend slightly more toward warmer color grades than CVD stones at equivalent production effort. Post-growth treatment additional HPHT processing at different conditions can convert some yellowish or brownish stones to near-colorless or colorless grades.

CVD: Chemical Vapor Deposition

CVD takes a fundamentally different approach. Instead of recreating mantle pressure, it builds diamond crystal layer by layer from a gas-phase carbon source at much lower pressures.

A thin diamond seed plate is placed in a vacuum chamber. The chamber is filled with a mixture of carbon-containing gas typically methane at approximately 1 to 10% concentration and hydrogen. Microwave radiation or other energy source ionizes the gas mixture, creating a plasma. In this plasma state, carbon atoms separate from the methane and deposit on the diamond seed in the diamond cubic arrangement. Hydrogen in the plasma prevents graphite from forming alongside the diamond.

The crystal grows upward from the seed surface at a rate of approximately 0.1 to 10 micrometers per hour depending on process conditions. Producing a 1-carat rough diamond through CVD takes one to four weeks. The growth produces a tabular crystal flat and roughly square that reflects the layer-by-layer deposition process.

CVD produces very high color grades more consistently than HPHT because the process excludes nitrogen effectively, reducing the yellow tint that nitrogen incorporation causes. Many of the highest color grade lab grown diamonds D-E-F colorless are CVD stones. CVD diamonds may show a slight brownish tint from certain structural defects that form during growth, but post-growth HPHT treatment removes this effectively.

HPHT vs CVD: Does It Matter for Buyers?

For most buyers making everyday jewelry purchase decisions, the production method matters less than the 4C grades and the certification body. A well-cut D-color VS1 CVD diamond and a well-cut D-color VS1 HPHT diamond are both excellent stones. The production method is noted on the grading report and is part of the stone's documentation, but it does not create a meaningful quality hierarchy for finished gems.

Some nuances worth knowing:

CVD tends to produce more colorless stones more consistently. If achieving D-F colorless grade is a priority and you are comparing stones at similar price points, CVD stones may offer better value in the top color tiers.

HPHT is more established the process has been commercially refined for longer. Some buyers and jewelers prefer HPHT stones for this reason, though the quality of both processes has converged considerably in recent years.

Post-growth treatment is common in both methods. HPHT treatment to remove brown tint from CVD stones, or HPHT treatment to upgrade color in some natural and lab grown stones, is an accepted industry practice. It should be disclosed on grading reports and is not considered a quality defect it is a production refinement step.

Neither method produces a better or worse diamond by the 4C criteria that matter for visual performance. Cut quality has far more impact on how brilliant and beautiful the finished stone looks than which growth method produced it.

The Seed Crystal and Why It Matters

Both HPHT and CVD start with a diamond seed a thin plate or small crystal of existing diamond that serves as the template for new growth. The seed's crystal orientation influences how the new diamond grows and can affect some quality characteristics of the finished stone.

For CVD diamonds, the seed plate is typically a few millimeters in size and is sliced away from the grown crystal before cutting. The seed is consumed in the production of each new diamond, so there is no meaningful "inheritance" of seed properties in the finished gem.

For buyers, the seed origin is not a meaningful quality distinction at the purchasing level. What matters is the finished stone's 4C grades as evaluated by the grading laboratory, not the seed's specific origin or orientation.

How Production Quality Is Verified

Both HPHT and CVD diamonds receive grading reports from independent gemological laboratories GIA, IGI, GCAL, and others that evaluate the finished stone by the same 4C criteria applied to natural diamonds.

The grading report specifies the production method (HPHT or CVD), confirms whether any post-growth treatment was applied, and evaluates cut, color, clarity, and carat weight. Reading the grading report correctly tells buyers everything material about the stone's quality.

One specific report element worth understanding: "As grown" on a CVD diamond report means no post-growth treatment was applied. "HPHT treated" or "irradiated" indicates treatment was used. Both treated and untreated stones are legitimate treatment is disclosed, not hidden. Some buyers prefer as-grown stones; others find the distinction irrelevant since the finished quality is what matters.

Our lab grown diamond collection includes certified stones with full specification documentation carat, color, clarity, cut, and production method on every listing.

Frequently Asked Questions

What is the difference between HPHT and CVD lab grown diamonds? HPHT replicates the high pressure and high temperature conditions that create natural diamonds in the earth's mantle. CVD builds diamond crystal layer by layer from a carbon-rich gas at lower pressure. Both produce genuine diamond. HPHT tends toward warmer colors in some production; CVD more consistently achieves colorless grades. Neither method produces a better diamond by 4C criteria.

Is CVD or HPHT diamond better? Neither is objectively better. Both produce genuine diamond with the same physical and optical properties. CVD may produce more colorless grades more consistently. HPHT is the more established process. For most buyers, the 4C grades and certification matter far more than the production method.

Can you tell if a diamond is HPHT or CVD? Not visually or through standard testing. Only advanced spectroscopic equipment in major gemological laboratories can identify the growth patterns that distinguish the two methods. The production method is disclosed on the grading report.

Are HPHT treated diamonds lower quality? Not inherently. HPHT treatment is a post-growth refinement process that improves color by removing certain structural defects. It is disclosed on grading reports and is an accepted industry practice. The finished stone's 4C grades reflect its quality after treatment.

How long does it take to grow a lab diamond? HPHT growth takes days to a few weeks depending on target size. CVD takes one to four weeks for a 1-carat rough crystal. Post-growth processing, cutting, and polishing add additional time before a finished stone is ready.

What is a diamond seed crystal? A small plate or crystal of existing diamond used as the template for new growth in both HPHT and CVD processes. The seed's crystal structure guides the arrangement of new carbon atoms. In CVD, the seed is sliced away from the grown crystal before cutting the finished gem.

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