CVD vs HPHT Lab Diamonds

CVD vs HPHT is the question that shows up once you start reading lab diamond grading reports. Both are ways to grow a real diamond in a lab, and both produce stones that are chemically and physically diamond. They just get there differently. This page explains each method in plain words, what each one can leave behind in the stone, and why, when you are choosing a ring, the finished grades matter much more than the growth method.

Every lab diamond starts with a seed

Both methods begin the same way, with a seed: a thin, flat slice of diamond. Carbon atoms attach to that seed and continue its crystal pattern, so the new growth is diamond too. Over a few weeks, the seed becomes a rough crystal large enough to cut. A cutter then shapes and polishes it exactly as they would a mined rough diamond.

The difference between CVD and HPHT is the environment around that seed while it grows.

How CVD works

CVD stands for chemical vapor deposition. The seed sits inside a sealed vacuum chamber. A carbon rich gas, usually methane mixed with hydrogen, is heated until it breaks apart into a glowing plasma. Carbon atoms drift down and bond onto the seed, building the diamond up in thin layers, a little like snow settling.

• Grows in layers, so the rough crystal is usually flat and tablet shaped.
• Runs at lower pressure than HPHT.
• Many CVD stones get a treatment after growth to improve their color. A good grading report says so in its comments.
• Commonly used for larger stones in the one to several carat range.

How HPHT works

HPHT stands for high pressure, high temperature. It copies the conditions deep in the earth where natural diamonds form. The seed is placed in a press with a carbon source and a molten metal that helps the carbon dissolve and move. Under great heat and pressure, carbon crystallizes onto the seed.

• Grows in all directions, so the rough often has a cube and octahedron shape.
• Can produce very white stones straight from growth.
• Can leave tiny metallic inclusions from the metal used in the press. In some stones that makes them respond to a strong magnet.
• Also used as a treatment, applied to some CVD diamonds after growth to improve color.

CVD vs HPHT side by side

Neither method is better across the board. A beautifully cut CVD stone and a beautifully cut HPHT stone of the same grades will look the same on your hand. A poorly cut stone of either kind will look dull.

Which one should you choose?

Honestly, most people should choose the stone, not the method. Here is how we approach it at the tray:

1. Start with shape and size. Pick what you love to look at.
2. Judge the cut with your own eyes. Brightness and even sparkle come first.
3. Check color in the metal you want, in daylight by the window and under the showroom lights.
4. Check clarity under the loupe. It should be eye clean at normal distance.
5. Then read the comments line for method and treatment, so you know the full story.

Some people do have a preference. A few like the idea of HPHT because it mirrors how natural diamonds form. Others prefer a CVD stone with no post growth treatment. If you have a preference, tell us and we will pull stones to match. If you do not, you are free to choose purely on beauty and budget.

Does the method change durability or care?

No. Once a lab diamond is cut and polished, CVD and HPHT stones wear the same way. Both are 10 on the Mohs scale, both resist scratches from everyday life, and both can chip if struck hard on an edge, just like a mined diamond. Care is the same too: warm water, a drop of dish soap and a soft brush every few weeks keep the sparkle up.

Color treatment after growth is permanent. It does not wash off, fade in sunlight or change with cleaning. A jeweler can steam clean, re-polish or reset either kind of stone safely. If you ever have a ring sized or a prong retipped, tell the bench jeweler it is a lab diamond, as you would with any stone, and they will handle it the normal way.

How to find the method on a report

On an IGI report, the growth method and any treatment usually appear in the comments section. You may see wording that names the process used and notes post growth treatment if there was any. GIA also grades lab grown diamonds, and its paperwork shows the report type clearly. Our guide to IGI certified lab grown diamonds walks through every line of a report, and our 4Cs guide explains the grades themselves.

See CVD and HPHT stones in person

The easiest way to stop worrying about method is to look at both. Use our loose lab grown diamond request to tell us the shape, carat, color, clarity and budget you have in mind, and add a note if you want to compare CVD and HPHT. We pull 3 to 5 matching stones and have them on the tray at 30 West 47th Street, Suite 806.

Still deciding between lab and mined? Read lab grown vs natural diamonds. Ready to look? Book a viewing or call (212) 642-4345. The showroom is a short walk from the B, D, F and M trains at 47-50 Sts Rockefeller Center.