HPHT diamonds are laboratory-grown diamonds created using controlled high-pressure and high-temperature conditions designed to support diamond crystal growth.
They are real diamonds in the sense that they have the same carbon-based atomic structure as naturally-occurring diamonds, but these diamonds do not originate from the earth.
The buyer in the UK should know how the HPHT process works because it is possible that the way the crystal was grown will be indicated on the grading report or the product description. However, it is hard to argue that the method used to grow the crystal is more important than the quality of the diamond itself for the sake of comparison.
What Does HPHT Mean in Diamonds?
HPHT stands for High Pressure High Temperature. The process imitates some of the forces that are present when a diamond is formed in nature but within a specialised machine, and not underground.
A small Diamond Seed is placed into a growth chamber alongside a carbon source. Very high pressure and temperatures are applied allowing carbon to crystallise around the seed forming a diamond.
The process is very controlled, however it doesn’t make exactly the same stones. All HPHT diamonds may have different characteristics such as colour, clarity, carat weight, proportions and many others.
This is why it is important when comparing hpht diamonds to look at the specifications of each diamond rather than the method it was grown .
Are HPHT Diamonds Real Diamonds?
Yes. HPHT diamonds are real diamonds. They possess the carbon crystal structure that is inherent to diamond and share many of its physical and optical properties. The only difference is the origin. Natural diamonds are formed geologically while lab diamonds are created in industrial settings. This is their only difference.
HPHT diamonds are not to be confused with cubic zirconium or moissanite, as they have different crystal structures and physical properties.
A consumer may not be able to distinguish between the two, but professionals can subject them to specialized tests and inspections to identify which one is which.
HPHT vs CVD Diamond Growth
The two major methods used to create laboratory-grown diamonds are HPHT and CVD, or Chemical Vapour Deposition.
| Feature | HPHT | CVD |
|---|---|---|
| Full name | High Pressure High Temperature | Chemical Vapour Deposition |
| Growth environment | High pressure and heat | Controlled gas-filled chamber |
| Carbon source | Carbon material surrounding a seed | Carbon-containing gases |
| Result | Laboratory-grown diamond | Laboratory-grown diamond |
| Quality | Depends on the individual stone | Depends on the individual stone |
CVD typically builds diamond material in layers from carbon-containing gases inside a controlled chamber. HPHT uses pressure and heat to support crystal formation.
Neither method is automatically better.
A well-cut HPHT stone can be more visually appealing than a poorly proportioned CVD stone, and the reverse is equally possible. Growth method should therefore be treated as one piece of information rather than a quality score.
How HPHT Diamonds Are Graded
Laboratory-grown diamonds can be assessed using the same core 4Cs framework used for natural diamonds: cut, colour, clarity and carat weight.
Cut affects light performance
Cut describes how proportions and man made diamonds influence the way a faceted diamond interacts with light. For many buyers, this can have a greater effect on visible brilliance than paying for extremely high colour or clarity grades.
Cut should not be confused with shape. Round, oval, emerald, cushion and pear describe shapes, while cut quality relates to how effectively the diamond has been fashioned.
Colour describes visible body colour
Diamond colour grades measure the amount of colour found or lack thereof in accordance to the grading system used.
Having a higher colour grade doesn’t necessarily mean it’s the best buy. Metal of the jewellery, setting style, shape of the diamond itself as well as personal taste can influence the outcome.
Clarity assesses inclusions and blemishes
Clarity grading looks at internal characteristics (inclusions) and external characteristics (blemishes)
Very high clarity grades can increase the price, but may not be visually apparent to the naked eye. As such, buyers should look at actual stones and seek the best value rather than simply buying the highest grade available.
Carat is weight, not size
The carat is a unit of weight. Two diamonds of the same weight can look different because of their shape, depth and proportions, which affect the surface area that is visible from above.
What Should a Grading Report Show?
An independent grading report can provide a structured description of the diamond. Depending on the laboratory and report format, it may include:
- carat weight
- colour grade
- clarity grade
- measurements
- polish
- symmetry
- fluorescence
- proportions
- report number
- laboratory-grown origin
Recognised laboratories such as IGI and GIA evaluate laboratory grown diamonds using their own reporting systems and methodologies.
A grading report should not therefore be considered as a financial valuation. It describes the characteristics of the diamond, but it does not provide any guarantee as to its resale value, future market demand or specific retail price.
Where a report number or laser inscription is available, buyers should also be able to check that the identification information matches the stone being offered.
Does HPHT Growth Affect Appearance?
The way a diamond is grown can effect some of the properties that specialist labs will identify, but regular buyers should pay closer attention to the finished diamond itself.
Proportions, quality of cut, transparency, inclusions, colour and overall brilliance are important.
Fluorescence may also feature on a grading report. This refers to the reaction of a diamond to ultraviolet light under specific conditions. The impact of this should be judged on a case--case basis, depending on the diamond itself, and should not be determined purely the term “fluorescence”.
The same goes for growth method. “HPHT” refers to how the diamond was grown, not whether the diamond will look beautiful when set in a ring.
Choosing an HPHT Diamond for an Engagement Ring
In the case of an engagement ring, it is better to consider the stone in conjunction with its setting.
It is essential to compare the size and shape of the centre-stone, the width of the band and the profile of the ring itself. Low or high profile settings dramatically change the wearing comfort of the ring, while solitaire or halo, pavé or bezel settings allow you to visually transform the appearance of the ring.
In addition, it is essential to choose the metal in which the ring is made. Thus, the use of platinum, white gold, yellow gold or rose gold will slightly change the appearance of the ring. The same refers to the selection of stones: the visual perception of the colour grade of the diamond depends to a considerable extent on the metal of the setting.
Therefore, users who are looking for information about lab-grown diamonds, buying from UK retailers such as Novita Diamonds, in their turn, should compare the characteristics of a diamond, its visual appearance, and the selected jewellery setting to find the best option for themselves instead of only focusing on the carat weight.
Checks to Make Before Buying
Before buying a lab created diamond, do not only rely on the headline specs when comparing the stones. Check that the product is clearly stated as laboratory-grown and if a grading report from an independent laboratory is provided. Compare measurements as well carat weight, because two equal-weighted diamonds can face up different.
For finished jewellery, also confirm:
- whether stated carat weight refers to the centre stone or total diamond weight
- the metal specification
- the origin of accent stones
- resizing terms
- return conditions
- care and servicing information
It is also a good idea to retain the grading report and purchase documentation together with the jewellery after the sale. These documents contain relevant identification information in case the jewellery requires servicing, insurance, valuation or resale.
An informed purchase is the result of comparing the individual diamond, its grading information, the jewellery design and the retailer’s stated policies rather than relying on the fact that HPHT or any other production method in itself defines quality.