Most people who buy a lab grown diamond do not know how it was grown. They know it was grown above ground rather than mined below it. They may know it has a certificate from the GIA or IGI. They probably do not know whether it was grown using HPHT, CVD, or MPCVD technology, and they almost certainly do not know why the difference between those three methods matters enormously.
It matters because the method of growth is one of the most significant factors in the quality, purity, and appearance of the finished stone. And because the method that produces the finest diamonds, MPCVD, is also the most expensive, most technically demanding, and least commonly used in mass production.
Diamonds of Cornwall uses MPCVD exclusively. Here is why.
The Three Methods of Growing a Diamond
HPHT: High Pressure High Temperature
HPHT was the first method humans used to grow diamonds. It was developed in the 1950s and works by mimicking the extreme pressure and heat conditions deep within the earth where natural diamonds form.
A carbon source, typically graphite, is placed in a press along with a metal catalyst, usually iron, nickel, or cobalt. The press subjects the material to pressures of up to 1.5 million pounds per square inch and temperatures of up to 1,500 degrees Celsius. Under these conditions, the carbon dissolves into the molten metal and crystallises as diamond around a seed crystal.
The fundamental problem with HPHT is the metal catalyst. Under the extreme stress of the process, atoms from the metal can become incorporated into the growing diamond crystal. This can give the diamond a yellowish or brownish tint, create magnetic properties, and introduce inclusions that affect clarity and brilliance. HPHT diamonds frequently require post-growth treatment to improve their colour, which adds cost and complexity without fully addressing the underlying quality limitations.
HPHT is widely used in mass production because the presses are relatively inexpensive and the process is well understood. It is not the method used by producers who prioritise quality above volume.
Standard CVD: Chemical Vapour Deposition
CVD was developed later than HPHT and uses a fundamentally different process. A diamond seed crystal is placed in a chamber filled with a carbon-rich gas, typically methane, which is then activated by a heat source to break the gas molecules apart. The freed carbon atoms fall onto the seed crystal and accumulate layer by layer, growing a diamond over a period of weeks.
Standard CVD typically uses electrically heated metal filaments to activate the gas. This is where the quality problem arises. The filaments operate under extreme stress and at very high temperatures, and atoms from the metal wires can enter the gas phase and contaminate the growing diamond. The result is often stones with a greyish or brownish tint, reduced brilliance, and a flat or lifeless appearance in person despite carrying a credible certificate.
CVD diamonds grown too quickly, which is the tendency in volume production facilities, can also develop crystal strain and graining that creates a blurriness visible under magnification and sometimes detectable to a trained eye in normal light.
Standard CVD produces better diamonds than HPHT on average, but it has significant limitations when optimised for volume and cost rather than quality.
MPCVD: Microwave Plasma Chemical Vapour Deposition
MPCVD is a refinement of the CVD process that eliminates the fundamental contamination problem of standard CVD. Instead of electrically heated metal filaments, MPCVD uses a microwave-generated plasma ball that hovers freely in the centre of the growth chamber without touching the walls or any metal surface.
Because the plasma is generated by microwave energy rather than by metal filaments, there is no source of metal contamination in the growth environment. The carbon-rich gas is activated cleanly and uniformly. The diamond grows in a controlled, uncontaminated environment that produces consistently pure crystals with exceptional optical properties.
The result is diamonds of Type IIA purity: the rarest and most valuable diamond type, characterised by an absence of nitrogen and a crystal structure so clean that the stones are exceptionally transparent, exceptionally hard, and exceptionally brilliant.
MPCVD is to diamond growing what a Michelin starred kitchen is to cooking. The fundamental ingredients are the same. The precision, the care, the time, and the result are in a completely different category.
Why MPCVD Produces Better Diamonds
The quality advantage of MPCVD over other diamond growing methods comes down to three things: purity, consistency, and control.
Purity
Because MPCVD eliminates the metal contamination risk that affects both HPHT and standard CVD, the resulting diamonds are purer at the crystal level. This translates directly into better colour, better clarity, and better brilliance in the finished stone. MPCVD consistently produces Type IIA diamonds. Other methods can produce Type IIA stones but do so less consistently and require more careful selection and rejection of substandard material.
Consistency
The microwave plasma environment in MPCVD is exceptionally stable and controllable. The temperature, pressure, gas composition, and plasma characteristics can all be monitored and adjusted with a precision that is not achievable with the cruder energy delivery mechanisms of HPHT presses or heated filament CVD systems. This consistency means that MPCVD produces diamonds that meet a high standard reliably rather than producing a mix of high and low quality stones that must be sorted afterwards.
Control
MPCVD gives the grower a level of control over the growth environment that allows for deliberate optimisation of diamond quality rather than simply hoping the conditions remain favourable. Growth rate, crystal orientation, and the introduction of trace elements for specific properties can all be managed with a precision that makes MPCVD the technology of choice for research institutions, specialist producers, and anyone for whom quality is more important than volume.
What Type IIA Actually Means
Diamond types are classifications based on the impurities present in the crystal structure. Type IA diamonds, which represent approximately 98% of all natural diamonds, contain nitrogen impurities in clusters throughout the lattice. This gives them a slight yellow tint and affects their optical properties.
Type IIA diamonds contain very little or no nitrogen. They are the purest form of diamond, structurally speaking, and represent only one to two percent of all natural diamonds. Their absence of nitrogen means they are exceptionally colourless, transmit light more efficiently than Type IA stones, and achieve a level of brilliance that is visibly different to a trained eye.
Historically, Type IIA diamonds were among the rarest and most prized stones in the world. Some of the most famous diamonds in history, including the Cullinan, the Koh-i-Noor, and the Elizabeth Taylor Diamond, are Type IIA. Their rarity in nature made them effectively inaccessible to anyone who was not extraordinarily wealthy.
MPCVD, done properly, produces Type IIA diamonds consistently. This is one of the most significant things about the technology. It democratises access to the finest diamond type that nature produces, making it available through a process that is better for the planet than mining and better for quality than alternative growing methods.
Every diamond grown by Diamonds of Cornwall using our MPCVD technology is Type IIA. This is not a grade we achieve occasionally. It is what our process produces by default. It is what MPCVD does when it is done properly.
MPCVD and the Environment
Beyond quality, MPCVD has important environmental advantages over alternative growing methods.
HPHT requires enormous mechanical presses that consume very large amounts of energy to generate the required pressures. The energy intensity of HPHT production is significantly higher than MPCVD on a per-carat basis.
Standard CVD using heated filaments also carries unnecessary energy overhead from the resistance heating required to maintain filament temperatures. MPCVD's microwave plasma is a more energy-efficient way of activating the growth process.
When combined with renewable energy, MPCVD offers the most energy-efficient route to the highest quality diamond available. This is the combination Diamonds of Cornwall has built: MPCVD technology powered by 100% renewable Cornish energy, producing Type IIA diamonds with the smallest possible carbon footprint before carbon removal is applied.
Frequently Asked Questions About MPCVD
Is MPCVD better than CVD?
Yes, in terms of the quality of diamond produced. MPCVD eliminates the metal contamination risk that limits the quality ceiling of standard CVD and produces Type IIA diamonds more consistently. It is more expensive and more technically demanding than standard CVD, which is why it is less commonly used in mass production.
Is MPCVD better than HPHT?
Yes. MPCVD produces cleaner, purer diamonds without the metal contamination and colour treatment issues associated with HPHT. HPHT has its uses in industrial diamond production where gem quality is not required, but for jewellery grade diamonds MPCVD is the superior method.
Can I tell if a diamond was grown using MPCVD just by looking at it?
A well-grown MPCVD diamond will typically have better colour, better brilliance, and better overall appearance than a comparable stone grown using HPHT or standard CVD. A trained gemmologist can often identify the growth method by examining the diamond under magnification. The certificate from the IGI or GIA will not always specify the growth method, which is why it is worth asking the retailer directly.
Why do not all lab grown diamond producers use MPCVD?
Cost and complexity. MPCVD reactors are significantly more expensive than HPHT presses and require more specialist expertise to operate. For producers optimising for volume and low cost, the capital investment and operational demands of MPCVD are difficult to justify. For producers optimising for quality, MPCVD is the only logical choice.
Enquire about a Diamonds of Cornwall -> diamondsofcornwall.com
Continue Reading
Blog: Who Is Diamonds of Cornwall? ->
Blog: Not All Lab Grown Diamonds Are Equal ->
Blog: What Carbon Negative Actually Means ->
Blog: Why We Grow Diamonds in Britain: The Sovereign Supply Chain Story ->
Blog: The Cornish Diamond: What Makes a Diamond Truly British? ->