HPHT Diamonds Explained Clearly

HPHT growth process of a lab-grown diamond
ROSY DIAMOND KNOWLEDGE

HPHT diamonds explained simply

HPHT uses high pressure and high temperature to grow a diamond crystal under controlled conditions.

Learn what role the diamond seed, carbon, and metal catalyst play—and why HPHT does not automatically indicate a quality grade.

FUNDAMENTALS

What does HPHT mean?

HPHT stands for High Pressure High Temperature.

In this growth process, a diamond seed, a carbon source, and a metallic solvent or catalyst system are placed in a special high-pressure cell.

Under very high pressure and high temperature, carbon can dissolve and crystallize as new diamond on the diamond seed.

Important HPHT initially describes the method used to create a lab-grown diamond. The term alone says nothing about the quality of the finished, cut stone.
HPHT pressure cell for growing a lab-grown diamond
THE GROWTH CELL

Pressure and temperature create the growth environment

The components are enclosed in a special cell inside a high-pressure press.

This creates the conditions under which carbon can be transported and crystallized onto the diamond seed.

  • diamond seed as the starting point
  • carbon source
  • metallic solvent or catalyst system
  • very high pressure
  • high temperature
CRYSTAL GROWTH

How does the carbon reach the diamond seed?

In the HPHT system, the carbon source is positioned in a slightly warmer area than the diamond seed.

The metallic medium helps dissolve carbon. The dissolved carbon moves through the growth environment toward the slightly cooler diamond seed.

There, it crystallizes and enlarges the existing diamond structure.

The result is crystal growth. The diamond is not cast or pressed merely to obtain the shape of a diamond.
Carbon, metal catalyst, and diamond seed during HPHT growth
STEP BY STEP

The HPHT growth process

1

Preparation

The diamond seed, carbon source, and metallic growth medium are arranged in the cell.

2

Growth

Pressure and temperature enable carbon to be transported to the diamond seed.

3

Crystal

Carbon crystallizes on the seed, and a larger diamond forms.

Uncut HPHT lab-grown diamond in rough crystal form
AFTER GROWTH

The HPHT rough crystal

After the growth process, there is not yet a finished jewelry diamond.

The rough crystal has its own growth form and must first be analyzed. Then it is planned how to create the most attractive possible cut diamond from it.

Cutting, shaping, and polishing can produce Round Brilliant, Oval, Pear, Cushion, or other shapes.

The final shape is created only during cutting. The growth process and the final jewelry shape are two different steps.
GEMOLOGICAL FEATURES

Can HPHT growth leave traces?

The special growth environment can produce features recognizable to gemologists. These may include characteristic growth structures or, in some stones, metallic inclusions.

Professional laboratories use these characteristics together with spectroscopic and other examination methods for identification.

This does not automatically mean poor quality. How pronounced individual characteristics are and which clarity grade a diamond receives depends on the specific stone.
IMPORTANT DISTINCTION

HPHT-grown and HPHT-treated are not the same

HPHT-grown

The diamond itself was grown using the High-Pressure-High-Temperature process.

HPHT-treated

A diamond that has already been grown was later exposed to HPHT conditions again, for example to alter certain color properties.

Why this distinction matters For example, a CVD diamond may undergo HPHT post-treatment after it has grown. In terms of its growth method, it remains a CVD diamond.
QUALITY

Is HPHT better or worse than CVD?

This cannot be answered in general terms.

HPHT and CVD are different methods of growing a lab-grown diamond. The finished stone’s visible quality, on the other hand, depends on its individual characteristics and the craftsmanship.

The 4Cs

  • Carat – Weight
  • Cut – Cut
  • Color – Color
  • Clarity – Clarity

Additional considerations

  • Measurements and proportions
  • Polish
  • Symmetry
  • Shape
  • Overall appearance
ROSY Tip Do not choose a diamond solely based on the designation HPHT or CVD. The specific stone is what matters.
GRADING REPORT

What can a laboratory report show?

An independent gemological report provides additional transparency about the characteristics and origin of an examined diamond.

  • Laboratory origin
  • Growth method
  • Carat weight and measurements
  • Color and clarity
  • Cut characteristics
  • Polish and symmetry
  • Possible indications of post-growth treatments
  • Additional comments or identification data
HPHT lab-grown diamond with a gemological grading report
ROSY Certificate Standard For a single lab-grown diamond of 0.50 ct or more, ROSY Lab Diamonds provides an independent IGI grading report as well as the ROSY product certificate.
BUYING GUIDE

What should I look for in an HPHT diamond?

1

View the diamond

Cut, proportions, and visual appearance are more important than the method name.

2

Compare the 4Cs

Consider carat weight, color, clarity, and cut as a complete picture.

3

Check the report

Read the information about laboratory origin, growth method, and possible treatments.

IN BRIEF

HPHT diamonds at a glance

  • HPHT means High Pressure High Temperature.
  • Growth begins on a diamond seed.
  • A carbon source supplies the material for the growing crystal.
  • A metallic medium supports carbon transport.
  • High pressure and high temperature enable growth.
  • After growth, a rough crystal is formed first.
  • HPHT-grown and HPHT-treated are different terms.
  • HPHT alone is not a quality grade.
  • An independent grading report provides additional transparency.
ROSY DIAMOND KNOWLEDGE

Understand HPHT. Assess quality correctly.

Also discover CVD diamonds and the complete journey from diamond seed to finished lab-grown diamond.

Discover diamond knowledge CVD diamonds explained How are lab-grown diamonds created?