Lab-grown diamonds have exploded in popularity in recent years as an ethical, affordable alternative to mined diamonds. One of the main methods for creating diamonds in a lab setting is called high pressure, high temperature (HPHT).
HPHT (High Pressure High Temperature) diamonds are created through a process that mimics the conditions deep within the Earth. This treatment can enhance the color and clarity of a diamond, but it is important to disclose this information when buying or selling to ensure transparency.
This article will explore what exactly HPHT diamonds are, how they are made, their characteristics, and whether they may be the right option for your fine jewelry needs.
What Are HPHT Diamonds?
HPHT diamonds are diamonds that are formed in a laboratory using high amounts of heat and pressure to simulate the conditions under which diamonds form naturally deep within the Earth.
The HPHT growth process was first developed in the 1950s and involves placing a diamond “seed” into a press device and subjecting it to temperatures as high as 2200°C and pressures over 1 million psi. As the seed is exposed to these extreme conditions, the surrounding carbon begins crystallizing onto the seed, growing it layer-by-layer into a larger diamond.
HPHT diamonds display the same atomic structure, crystal arrangement, chemical composition, optical properties, and hardness as naturally occurring diamonds. In fact, gemological laboratories certify HPHT diamonds using the same 4Cs grading criteria as mined diamonds: cut, color, clarity, and carat weight. The only way to distinguish an HPHT diamond is through advanced spectroscopic testing.
Differences between HPHT lab-grown diamonds and natural mined diamonds.
Here’s a table that highlights the key differences between HPHT lab-grown diamonds and natural mined diamonds:
|HPHT Lab-Grown Diamonds
|Natural Mined Diamonds
|Created in a laboratory under controlled conditions
|Mined from deep within the Earth
|Typically 30-50% less expensive than mined diamonds
|Prices can vary significantly based on size, quality, and market
|Significantly lower carbon emissions, water usage, and land disruption
|High environmental impact due to mining, including land disturbance and habitat destruction
|Generally lower resale value compared to mined diamonds
|Mined diamonds often retain or appreciate in value over time
|Can achieve high clarity grades (VVS or IF) and excellent color
|Quality varies widely based on natural factors, but some natural diamonds can achieve exceptional quality
Compared to mined diamonds of equivalent size and quality, HPHT lab diamonds have a significantly lower cost. Their affordable price point makes them ideal for use in fine jewelry.
HPHT Diamond Size and Cost Comparison
|Carat Size (CT)
|HPHT Lab-Grown Diamond Price Range ($)
|Natural Mined Diamond Price Range ($)
|0.50 – 0.75
|$500 – $2,000
|$1,000 – $5,000
|1.00 – 1.50
|$2,000 – $7,000
|$5,000 – $15,000
|2.00 – 2.50
|$7,000 – $15,000
|$15,000 – $40,000
|3.00 – 3.50
|$15,000 – $30,000
|$40,000 – $80,000
|4.00 – 4.50
|$30,000 – $50,000
|$80,000 – $150,000
The HPHT Process for Growing Diamonds
The first step in creating HPHT diamonds is selecting a tiny sliver of diamond to use as the seed crystal. The diamond seed is carefully cleaved along the crystal plane and then placed in the center of the press.
The press consists of an anvil made from a cemented carbide cylinder and a binding agent. It contains a hollow center in which the diamond seed and graphite source material are placed. The press applies gradual increasing pressure, eventually reaching over 1.5 million psi.
At the same time, the temperature inside the press is slowly increased. Common temperature ranges are from 1300-2200°C, with an ideal range between 1500-1700°C. This high heat liquefies the graphite.
As pressure and temperature increase, the liquefied graphite starts crystallizing onto the diamond seed. The pressure keeps the carbon tightly compacted so that the diamond crystal structure results as the carbon solidifies.
New layers of diamond slowly precipitate from the liquefied graphite and the diamond seed grows larger. Typical growth rates are 1mm per hour. The total growing time ranges from 1 to 4 weeks.
At the end of the cycle, the press is slowly cooled and the pressure is reduced. Then the newly formed HPHT diamond can be removed for cutting and polishing.
Growth Times for HPHT Diamonds per Carat Weight
|Carat Size (CT)
|Typical Growth Time (Weeks)
|0.50 – 1.00
|1 – 2 weeks
|1.00 – 2.00
|2 – 3 weeks
|2.00 – 3.00
|3 – 4 weeks
|3.00 – 4.00
|4 – 5 weeks
|4.00 – 5.00
|5 – 6 weeks
Applying Color Treatment with HPHT
In addition to growing diamonds, the HPHT process can also be used to alter the color of some diamonds. Diamonds containing structural irregularities or certain impurities may be HPHT treated to improve their color grade.
Diamonds types Ia and Ib are the best candidates for HPHT color enhancement. When exposed to the high pressure and temperatures inside the HPHT devices, negatively tinted nitrogen compounds can be converted into positive ones. This makes the diamond less yellow, brown, or gray. The result is a more colorless or blue/pink diamond.
However, HPHT cannot alter all diamonds. Diamonds that already have the maximum possible color saturation or contain other impurities will not have their color changed by HPHT treatment.
Benefits of Choosing HPHT Lab Diamonds
There are several potential benefits associated with opting for an HPHT diamond over a mined diamond:
- More affordable: HPHT diamonds usually cost 30-50% less than an equivalent natural diamond. Greater size can be obtained for the same budget.
- High clarity: The controlled lab conditions allow for diamonds with Very Very Slightly Included and Internally Flawless clarity to be produced. Natural diamonds rarely achieve this.
- Treatable color: While not all HPHT diamonds undergo treatment, the process can produce more colorless diamonds.
- Eco and conflict-free: Lab diamonds are not associated with the environmental and ethical concerns that come with diamond mining.
- Efficiency: It takes a few weeks to grow a lab diamond, compared to over a billion years underground.
For many consumers, the combination of ethical sourcing, superior quality, and lower cost makes HPHT lab diamonds an excellent choice.
HPHT Diamonds and The 4Cs
Let’s examine how HPHT diamonds perform when graded according to the standard 4Cs: cut, clarity, color and carat weight.
- Cut: HPHT diamonds can be cut and polished into the full range of shapes. Precision cutting is used to maximize brilliance and sparkle.
- Clarity: As mentioned earlier, the controlled conditions inside the HPHT devices facilitate extremely clear diamonds without imperfections and inclusions. Most are VVS or IF.
- Color: Some HPHT diamonds will have less color than naturally occurring ones, especially after treatment. However, very rare colors like red or pink do not occur.
- Carat: HPHT diamonds typically range from 0.01 cts up to around 5 cts. Large diamonds are not impossible, but do take longer to produce.
Overall, HPHT diamonds can achieve the same 4Cs grades as mined diamonds. In some cases, such as clarity, they may surpass what is available from the earth!
Comparison of Clarity Grades
|HPHT Lab-Grown Diamonds (%)
|Natural Mined Diamonds (%)
|0.01% – 0.1%
|Internally Flawless (IF)
|0.1% – 0.5%
|Very Very Slightly Included (VVS1-VVS2)
|0.5% – 2.0%
|Very Slightly Included (VS1-VS2)
|2.0% – 6.0%
|Slightly Included (SI1-SI2)
|6.0% – 15.0%
|15.0% – 50.0%
What to Look for When Shopping
Reputable diamond sellers will clearly disclose if a diamond was created in a laboratory using HPHT or other methods. Some ways to identify HPHT diamonds:
- Diamond certificate from a gem lab like GIA, AGS, EGL clearly states “HPHT-grown”.
- Online diamond listing states “Lab-Grown” or “Created”. Should disclose if HPHT method used.
- Jeweler verbally discloses stone is lab-grown if you ask.
If you wish to independently verify, lab reports from advanced spectroscopic tests like FTIR or Raman spectroscopy can detect the differences between HPHT and mined diamonds.
Where to Buy HPHT Lab Diamonds
Here are some reputable retailers to consider when shopping for HPHT diamonds:
- Online retailers like Clean Origin, Ada Diamonds, and Brilliant Earth specialize in lab diamonds, including HPHT. Large selections and custom design services.
- Department stores like Macy’s, Bloomingdale’s, Helzberg, and Zales are now carrying HPHT diamond engagement rings and jewelry in many locations.
- Local jewelers may have relationships with specific diamond vendors and may be able to source HPHT diamonds through their contacts.
- Diamond search sites like James Allen and Blue Nile now have filters where you can view only HPHT diamond options.
- Luxury brands like Pandora and Swarovski use lab diamonds, including HPHT, in some of their jewelry lines.
Be sure to review authentication documents when making any significant purchase. Reputable dealers will provide a lab diamond certificate from a 3rd party grader like GIA.
HPHT Resale Value
Like most lab diamonds, HPHT diamonds have a lower resale value compared to mined diamonds. Potential buyers may be concerned with authenticity or simply prefer natural stones. Expect to recoup around 30-50% of the original purchase price if selling.
So HPHT diamonds are best suited for buyers planning to keep their stone long term rather than as an investment.
However, if you decide to upgrade your ring in the future, some retailers will offer partial credit for HPHT diamonds, especially if trading up for a more expensive mined diamond.
Comparing HPHT vs CVD
The two most popular methods for lab diamond creation are HPHT and chemical vapor deposition (CVD). Here’s how they differ:
- HPHT simulates the high heat and pressure conditions deep underground. CVD deposits carbon molecules layer-by-layer on a substrate.
- HPHT equipment has a higher upfront investment cost. CVD machines are more affordable for small startup production.
- CVD allows better control over impurities. HPHT diamonds have a higher rate of defects and inclusions.
- CVD is slower at producing large diamonds over 2 carats. HPHT can create 5+ carat diamonds more efficiently.
- HPHT introduces less surface strain. CVD layering creates more fractures and cleaving tendencies.
HPHT vs CVD methods for Lab-Grown Diamonds
|HPHT (High Pressure High Temperature)
|CVD (Chemical Vapor Deposition)
|Simulates high heat and pressure conditions to grow diamond crystals on a diamond “seed.”
|Deposits carbon molecules layer-by-layer on a substrate, typically a diamond wafer or seed.
|Faster growth compared to CVD, typically weeks to a few months.
|Slower growth, especially for larger diamonds, can take months to years.
|Produces high-quality diamonds with fewer impurities and inclusions.
|Requires careful control to minimize impurities; can result in excellent quality.
|Control Over Impurities
|Fewer impurities due to the controlled environment.
|Better control over impurities, resulting in high purity diamonds.
|Large Diamond Production
|Efficient for creating larger diamonds exceeding 10 carats.
|Slower growth limits the production of large diamonds over 2 carats.
|Moderate energy consumption.
|Relatively low energy consumption.
|Lower environmental impact compared to traditional mining.
|Lower environmental impact due to reduced energy and water usage.
|Lower cost compared to CVD for producing larger diamonds.
|Higher cost for larger diamonds due to longer growth times.
Overall, the methods are complementary with some trade-offs. Both produce high quality diamonds indistinguishable from mined diamonds except under microscopic scrutiny.
Are HPHT Diamonds “Real”?
This is a common question buyers have regarding lab-grown diamonds. Since they are chemically and optically identical to earth-mined diamonds, HPHT diamonds are indeed real diamonds. They are not imitations, simulants, or substitutes. Classifying them as “fake” is inaccurate and outdated.
The distinction is their origin. HPHT and other lab diamonds are man-made, while mined diamonds originate deep within the earth. Both types are real diamonds and contain the same crystalline carbon structure.
Think of it like two wines from the same grape varietal. One was cellared underground naturally. The other was cellared above ground under controlled conditions. Both are real wines, just made differently!
Are HPHT Diamonds Eco-Friendly?
Because there is no mining involved, lab-grown diamonds have far less environmental impact than mined diamonds. Exact numbers vary by study methods, but HPHT diamonds generate around 5-15x less CO2 emissions and use 200x less water compared to mining practices.
However, HPHT does require high amounts of energy to achieve the heat and pressure levels. Responsible companies will use renewable or low-carbon energy sources to further reduce the ecological footprint.
So, yes, HPHT diamonds are a much more sustainable option compared to mined diamonds. especially as renewable energy use increases.
Environmental Impact Data
Here are some general data points to highlight the differences between HPHT diamond production and traditional diamond mining in terms of CO2 emissions, water usage, and energy consumption.
|HPHT Diamond Production
|Traditional Diamond Mining
|Lower emissions due to controlled processes and less transportation. Approx. 2,500 kg CO2 per carat produced.
|Higher emissions due to energy-intensive mining and transportation. Approx. 15,000 kg CO2 per carat produced.
|Relatively low water consumption. Approx. 70-140 liters per carat produced.
|High water usage in mining, including extraction and processing. Approx. 1,000,000 liters per carat produced.
|Moderate energy consumption for the HPHT process. Approx. 250 kWh per carat produced.
|High energy consumption in mining, including drilling and hauling. Approx. 1,500 kWh per carat produced.
Here are some comments from a few of my clients who I helped to buy HPHT lab-grown diamonds…
“I recently got engaged with an HPHT lab-grown diamond ring, and I couldn’t be happier! The diamond’s brilliance and sparkle are absolutely stunning. Knowing that it’s ethically sourced and environmentally friendly makes it even more special. I highly recommend HPHT lab diamonds to anyone looking for a beautiful and responsible choice.”
“I decided on an HPHT lab-grown diamond for my wedding band, and I’m so pleased with my choice. The diamond’s clarity is exceptional, and it pairs perfectly with my existing engagement ring. It’s reassuring to know that I’m wearing a diamond that’s both stunning and ethical. I’ve recommended HPHT lab diamonds to my friends already!”
The Bottom Line
HPHT diamonds offer an affordable, eco-friendly alternative to mined diamonds. Thanks to recent advances, their quality now rivals and even surpasses mined diamonds. Their visual appearance is stunning and indistinguishable to the naked eye.
For jewelry shoppers concerned with ethics and costs, HPHT lab diamonds are an excellent choice.
While the resale value lags behind mined diamonds, their substantially lower upfront cost makes them ideal for buyers planning to retain their stone for many years to come.