Full Descriptions of HPHT Rough Diamonds

1. Basic Definition

HPHT (High Pressure High Temperature) rough diamonds are lab-grown unpolished diamond crystals synthesized artificially by replicating the extreme geological conditions where natural diamonds form deep within the Earth’s mantle. Chemically, physically and optically they are genuine crystalline carbon diamonds (cubic diamond lattice), identical in material properties to mined natural rough diamonds; they are not simulants like cubic zirconia or moissanite.

2. Production Principle & Manufacturing Process

Core reaction conditions

• Pressure: 5–6 GPa (~50,000 atmospheres), equivalent to geological pressure 150 km underground
• Temperature: 1300–1600 °C
• Raw materials: Tiny diamond seed crystal, high-purity graphite (carbon source), molten metal flux/catalyst (nickel, iron, cobalt alloy) inside sealed reaction capsules in hydraulic cubic/BARS presses..

3. Features of HPHT Rough Diamonds

The rough diamonds produced by our HPHT cubic press machine equipment have good crystal shape and are hexahedral. 1A grade diamonds have good color, high clarity, few impurities, and a crystal yield of 40-43%. 1A grade diamond rough has relatively few impurities or is only on the rough surface, which can be removed by grinding.

4. The HPHT Diamonds VS CVD Diamonds

HPHT Advantages and Disadvantages

Advantages: Native high-color (D/E) diamonds in small to medium carats, no secondary color alteration required, clean certificate with no treatment notes; Mature mass production, low cost, the best value for money for diamonds under 1 carat; Crystal growth pattern closest to natural diamond crystal form; Mature and stable technology for blue lab-grown diamonds and yellow lab-grown diamonds.

Disadvantages: Metal catalyst residue is easy to remain, some may have weak magnetism, small black metal inclusions; Larger sizes (2ct and above) are more difficult to grow, have a lower yield rate, and are more expensive; Color may be uneven.

CVD Advantages and Disadvantages

Advantages: Pure, metal-free, and non-magnetic growth environment, easier to stabilize high-clarity VVS; Extremely strong mass production capacity for very large carats (2ct~20ct), best value for money for large carats; Pure Type IIa diamonds, suitable for high-end collections and custom jewelry; No metal impurities, better stability for later setting and laser engraving.

Disadvantages

Most colorless CVD requires HPHT color correction, and the certificate will indicate the heat treatment;

Small carat (within 1ct) are generally priced higher than HPHT;

Improper treatment of the original brown base may result in a very small risk of slight color reversion later (this is generally controllable by reputable manufacturers).