Lab-grown diamonds are gaining popularity among modern jewellery shoppers as a sustainable and ethical gemstone choice. Grown from a diamond seed in a laboratory setting, these diamonds have similar optical, chemical, and physical characteristics to natural ones. When purchasing lab-grown diamonds, shoppers may come across the terms HPHT and CVD. Understanding the differences between HPHT and CVD diamonds, along with their unique qualities, can help you decide which type best suits your preferences.
High Pressure High Temperature (HPHT) diamonds are created using a method that mimics the conditions within the Earth’s mantle. A diamond seed is placed in a chamber along with a carbon source. When the chamber is subjected to high temperature and pressure, the carbon crystallises around the seed and forms a diamond.
Chemical Vapour Deposition (CVD) diamonds are created in a low-pressure chamber. In this chamber, a carbon-containing gas such as methane is vaporised. The resulting gas is then ionised into a plasma, which deposits carbon atoms onto a diamond seed. The carbon atoms eventually arrange themselves into a crystalline structure and form a diamond.
The distinct methods used to produce HPHT vs CVD diamonds result in stones with different characteristics. Here are some comparisons between them:
Both HPHT and CVD lab-grown diamonds can produce diamonds with varying colour grades. HPHT diamonds used to occasionally exhibit a yellow or brownish tint from the presence of nitrogen impurities, but technological advancements have helped to yield highly colourless HPHT diamonds. Some HPHT-grown diamonds may also have a faint blue tint due to the presence of boron. Meanwhile, CVD-grown diamonds are often colourless as well, though many undergo post-growth treatment to improve colour and clarity.
Additionally, HPHT diamonds often show geometric colour zoning, which refers to angular patterns due to the uneven distribution of nitrogen. Natural diamonds may show zoning, but geometric patterns like those seen in HPHT diamonds are most commonly associated with synthetic stones.
HPHT and CVD diamonds may have different graining, inclusions, and strain patterns due to their different growth process. HPHT diamonds may contain metallic inclusions from trapped undissolved metal catalysts. These inclusions may appear black and opaque in transmitted light, but show a lustre in reflected light.
As CVD diamonds are grown from gas, they do not have metal inclusions. Instead, they may contain small dark specks of graphite and banded strain patterns that originate from the gas-deposition process. HPHT diamonds usually show little to no strain because they grow in a controlled environment.
HPHT and CVD diamonds interact differently with ultraviolet (UV) light, and their resulting fluorescence often occurs in a distinctive pattern. Most colourless and near-colourless HPHT diamonds do not usually show fluorescence, but may glow for a short time after the UV lamp is turned off. This is known as phosphorescence. Meanwhile, CVD synthetic diamonds may show a striped fluorescence pattern in green, yellow-green, yellow, orange, or red. These patterns do not reduce the diamond’s intrinsic quality or optical performance.
As both types of lab-grown diamonds are virtually identical to natural diamonds, they have comparable durability. This also makes both HPHT and CVD diamonds suitable for various types of jewellery, including high-carat lab-grown diamond rings. However, do note that any type of diamond can still fracture due to impact and should be worn with care.
There is no definitive answer to whether an HPHT or CVD diamond is better, as both methods can produce diamonds that are comparable to natural ones. If you have ever wondered, “What are lab-grown diamonds and which one should I choose?”, it is best not to consider only the production method, but more importantly the qualities you seek in an individual stone and how it can match your desired design.
Planning to shop for a diamond engagement or wedding ring with a unique design that reflects your love story? Ling Jewellery is here to help you craft lab-grown and natural diamond rings that suit your aesthetic preferences and budget. Get in touch with us and let us help you create a bespoke diamond ring today!
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