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HPHT Diamond Guide

This guide provides a comprehensive look into High-Pressure High-Temperature (HPHT) lab diamonds, their creation process, and how they compare to CVD lab diamonds.

What Is a HPHT Diamond?

Lab-grown diamonds are becoming increasingly popular, with HPHT (High-Pressure High-Temperature) diamonds as one of the two primary techniques to create lab diamonds. An HPHT diamond is a type of lab-grown diamond created by replicating the natural process that forms diamonds deep within the Earth's mantle. By exposing carbon to high pressure (approximately 5–6 GPa) and extreme temperatures (1,300–1,600°C) within a controlled environment, diamond crystals are formed. HPHT diamonds are chemically, optically, and physically identical to natural diamonds, making them an attractive choice for those seeking an ethical and affordable option.

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HPHT vs. CVD

CVD (Chemical Vapor Deposition) and HPHT are two methods for creating lab-grown diamonds, but they differ significantly in approach. 

Formation Method

HPHT replicates Earth's natural diamond formation, while CVD grows diamonds layer by layer in a gas-filled chamber. 

Diamond Size

HPHT is generally better for producing smaller, higher-quality diamonds, while CVD is suitable for larger diamonds. 

Inclusions

HPHT diamonds may contain metal inclusions due to the catalyst used, whereas CVD diamonds typically show fewer inclusions. It's important to note that lab diamonds undergo the same grading process as natural diamonds, including an assessment of the four Cs. 

Color Quality

HPHT diamonds often require less post-growth color treatment compared to CVD diamonds.

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HPHT Diamond Process

The HPHT process involves three key stages: 

  1. Creating the Environment: A specialized High-Pressure High-Temperature diamond machine includes a cell made up of three parts: The top layer contains the carbon material; the middle layer holds the metal catalyst, such as nickel or cobalt; and the bottom layer is where the diamond seed crystal is placed.  
  2. Diamond Formation: This capsule is subjected to extremely high pressure and heat. The carbon begins to crystallize, forming diamond structures, with the catalyst accelerating this process. 
  3. Cooling and Cutting: Once the diamond crystals have formed, the environment is slowly cooled, and the diamonds are extracted, cut, and polished.

This process closely mimics the natural formation of diamonds, which occurs over billions of years beneath the Earth's surface.

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HPHT Diamonds vs. HPHT Color Treatment

HPHT diamonds are often confused with HPHT-treated diamonds. While HPHT diamonds are grown in a lab, HPHT color treatment refers to a process used to enhance the color of natural or lab-grown diamonds. 

  • HPHT Lab-Grown Diamonds: These are created entirely in a lab using the HPHT process. 
  • HPHT-Treated Diamonds: These are natural or lab-grown diamonds subjected to HPHT conditions to improve their color, typically turning brownish diamonds into colorless or near-colorless ones. 

The key difference is the purpose: HPHT lab diamonds refers to the growing process (which could also include improvements to the diamond’s color), whereas HPHT-treated diamonds indicates that the gemstone has undergone an additional process for color enhancement as part of the growth process.

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How to Identify HPHT Diamonds

Identifying an HPHT diamond involves specialized tools and techniques. Key methods include:

 

  • Spectroscopy: Gemological labs analyze light absorption patterns unique to HPHT diamonds. 
  • Inclusions: HPHT diamonds may exhibit metallic inclusions, visible under magnification. 
  • Certification: Reliable certifications from organizations like GIA or IGI clearly state whether a diamond is HPHT-grown. 


The differences between CVD-grown diamonds, HPHT-grown diamonds, and natural diamonds are undetectable to the naked eye. At Brilliant Earth, we offer lab reports on all our diamonds for more information on a diamond’s origin and characteristics.

HPHT Diamond FAQ

What does HPHT stand for?

HPHT stands for "High-Pressure High-Temperature," describing the conditions used to grow or treat diamonds.

Are HPHT diamonds real?

Yes, HPHT diamonds are real diamonds. They share the same chemical composition, hardness, and brilliance as natural diamonds.

Do HPHT diamonds pass a diamond tester?

Yes, HPHT diamonds pass diamond testers. These devices detect the thermal conductivity of diamonds, which is identical in natural and lab-grown varieties.

What is HPHT diamond treatment?

Not to be confused with HPHT diamonds, HPHT diamond treatment enhances the color of diamonds by exposing them to high-pressure and high-temperature conditions. It’s important to note that HPHT treatment to CVD diamonds is commonly used and irreversible.

How long does it take to make an HPHT diamond?

Creating an HPHT diamond typically takes a few days to a few weeks, depending on the desired size and quality.

How are HPHT diamonds graded and certified?

HPHT diamonds are graded and certified using the same criteria as natural diamonds: the 4 Cs (Cut, Color, Clarity, Carat). Certifications from GIA, IGI, or HRD ensure their quality and authenticity.

What is the price of HPHT diamonds?

Because they are lab grown, HPHT diamonds are typically more affordable than natural diamonds of similar quality. Prices vary based on size, cut, and clarity.