CVD vs HPHT Diamonds — What's the Difference?

nishalgems
May 7
5 min read

A complete guide for buyers, jewellers & traders

CVD vs HPHT lab-grown diamond comparison guide by Nishal Gems Surat

If you've been researching lab-grown diamonds, you've almost certainly come across two abbreviations — CVD and HPHT. Both are methods used to grow diamonds in a laboratory. Both produce real, certified diamonds. But they work very differently, and the stones they produce have distinct characteristics.

At Nishal Gems, we specialise in CVD diamonds — and we've been manufacturing and trading them for over five years. So we know this topic inside out. In this guide, we'll explain exactly what CVD and HPHT mean, how each process works, and what the difference means for you as a buyer.

What Does CVD Mean?

CVD stands for Chemical Vapour Deposition.

In this process, a thin slice of diamond — called a diamond seed — is placed inside a sealed vacuum chamber. The chamber is then filled with carbon-rich gases, typically a mixture of methane and hydrogen. The gases are activated using microwave energy or a similar heat source, reaching temperatures of around 800–1,000°C.

At this temperature, the gas molecules break apart and free carbon atoms are released. These carbon atoms settle onto the diamond seed, layer by layer, slowly building up a diamond crystal — atom by atom — over a period of days to weeks depending on the desired size.

Once the rough diamond has grown to the required size, it is removed from the chamber and sent for cutting and polishing — exactly like a mined diamond.

The CVD process was developed in the 1980s and has become the dominant method of lab-grown diamond production globally, particularly in India and the United States.

CVD chemical vapour deposition lab-grown diamond growing process Nishal Gems

What Does HPHT Mean?

HPHT stands for High Pressure High Temperature.

This method directly mimics the natural conditions under which diamonds form deep inside the earth — extreme pressure and extreme heat applied to carbon over time.

In the HPHT process, a carbon source (typically graphite) is placed alongside a small diamond seed inside a specially designed press. The press applies enormous pressure — around 1.5 million pounds per square inch — and heats the material to approximately 1,400–1,600°C. Under these conditions, the carbon melts and begins to crystallise around the diamond seed, forming a new diamond.

The HPHT process was the first method used to grow gem-quality synthetic diamonds, developed by General Electric in the 1950s. It is still widely used today, both for growing new diamonds and for treating existing diamonds to improve their colour.

CVD vs HPHT — A Direct Comparison

	CVD	HPHT
Full name	Chemical Vapour Deposition	High Pressure High Temperature
How it works	Carbon gas deposits onto a seed	Carbon crystallises under extreme pressure & heat
Temperature	800–1,000°C	1,400–1,600°C
Pressure	Low pressure (vacuum)	Extremely high (~1.5M psi)
Growth time	Days to weeks	Days to weeks
Crystal shape	Cubic / flat plate	Cuboctahedral
Typical colours produced	D–J white, Type IIa	Various, including fancy colours
Post-growth treatment needed?	Sometimes (for colour)	Sometimes (for colour)
Common inclusions	Graphite, pinpoints	Metallic flux, black inclusions
Equipment size	Moderate	Very large industrial presses
Used at Nishal Gems?	✅ Yes	✗ No

The Key Differences Explained

1. How They Grow

CVD builds a diamond from the outside in — depositing carbon one atomic layer at a time onto a seed's surface. It's slow, precise, and highly controlled. HPHT forces a phase transformation — applying so much heat and pressure to carbon that it has no choice but to become diamond. Both produce real, gem-quality stones.

2. Colour & Purity

CVD diamonds are particularly well-known for producing Type IIa diamonds — the purest form of diamond, with virtually no impurities. Less than 2% of all mined diamonds are Type IIa. In CVD production, this grade is achievable more consistently.

Nishal Gems Insight

CVD sometimes produces a slight brown or grey tint in as-grown stones. A brief HPHT treatment removes this — it's a standard, accepted process fully disclosed on the certificate, comparable to cutting and polishing.

3. Inclusions

CVD diamonds: Graphite pinpoints, strain patterns, cloud-like graining
HPHT diamonds: Metallic flux inclusions, black carbon, strain patterns

In a VS1 or VS2 graded stone, neither type is visible to the naked eye. A trained gemologist using specialist equipment can identify the growth method from these inclusion types.

Diamond clarity inclusions under magnification VS1 lab-grown diamond Nishal Gems

4. Does the Growth Method Affect Price?

At equivalent quality grades, CVD and HPHT diamonds are similarly priced. Price is driven by the 4Cs — not the growth method. Both are 50–75% less expensive than mined diamonds of equivalent quality.

Does It Matter Which Method Was Used?

For most buyers — no, it does not matter. A 1.50ct, G colour, VS1 clarity, Excellent cut CVD diamond is chemically, physically, and optically identical to the same grades in HPHT. Both are real diamonds. Both are certified. Both sparkle identically.

The growth method matters for jewellers, gemologists, and traders who need to understand what they are buying. For the end buyer, what matters is the certificate — which always specifies the method.

HPHT Treatment vs HPHT Growth — Don't Confuse Them

HPHT is used both as a growth method (creating new diamonds) and as a treatment method (improving colour of existing diamonds). When applied as a treatment to mined or CVD-grown diamonds, it must be disclosed on the grading certificate. It does not reduce the diamond's authenticity or value.

Always Ask For

An IGI or GIA grading certificate. It will always disclose the growth method (CVD or HPHT) and any treatments applied. This is your guarantee of transparency.

Why Nishal Gems Chose CVD

Consistency — Precise control over the growth environment. Consistent colour, clarity, and size every time.
Purity — CVD regularly produces Type IIa diamonds — the finest classification of diamond purity.
Traceability — Every diamond is traceable to our Surat facility. Our clients always know the origin of their stone.
Expertise — Over 30 years in the diamond industry. CVD is our specialisation, not a sideline.

Frequently Asked Questions

Is a CVD diamond better than an HPHT diamond?

Neither is objectively better. Both produce real, high-quality diamonds. The differences are in the growth process and inclusion types — not in the beauty or value of the finished stone.