Synthetic, man-made diamonds (also known as lab grown diamonds) are increasingly preferred in the jewellery and industrial industry to replace natural diamond supply. These are not mere imitations; they are chemically, physically, and optically identical to diamonds. The fundamental distinction lies in their genesis: one forms deep within the Earth’s mantle over billions of years under immense heat and pressure, while the other is cultivated in a controlled laboratory environment over a period of weeks or months.
In this blog, we’ll examine the diamond manufacturing process, specifically focusing on High Pressure High Temperature (HPHT) and Chemical Vapor Deposition (CVD) as the two primary methods.
What are the Ingredients for Lab Grown Diamonds?
There are two fundamental components for the manufacturing of lab grown diamonds regardless of the specific method employed: a diamond seed, and a source of carbon.
A diamond seed is a tiny, pre-existing diamond crystal. The seed can be a thin slice of natural diamond or it can be a synthetic diamond obtained from previous growths. This seed acts as a crucial template, providing the necessary crystalline structure upon which the new carbon atoms can bond and meticulously arrange themselves into the diamond lattice.
The carbon source provides the elemental building blocks – the carbon atoms – that will form the new diamond material. The carbon source in HPHT is usually high-purity graphite. In the CVD process, carbon rich gases, primarily methane (CH4) are used, and they are often mixed with hydrogen and traces of other gases.
Method 1: High Pressure High Temperature (HPHT) Synthesis
HPHT was the first commercially successful diamond manufacturing process, producing synthetic diamonds under the same conditions as natural diamond formation in the Earth’s mantle. The steps are as follows:
- Preparation: A small diamond seed crystal is carefully placed at the bottom of a specially designed capsule or growth cell. The capsule also contains a source of high purity carbon (usually graphite) and a metallic catalyst or flux. The flux, which is usually a proprietary mixture of metals such as iron, nickel or cobalt, is essential in dissolving the carbon source and greatly reduces the high temperatures and pressures that are required to form diamonds.
- Pressurization and Heating: The capsule is placed into a large mechanical press that can generate very high pressures. The main types of presses are the belt press (the original option), the cubic press (which applies pressure using six anvils), and the split-sphere (BARS) press, which is particularly effective for producing large, high-quality single crystal diamonds. The growth chamber is then subjected to pressures of around 5 to 6 GPa, or 870,000 pounds per square inch, and heated to temperatures of between 1,300°C and 1,600°C.
- Dissolution and Crystallization: Under these extreme conditions, the metallic flux melts, dissolving the carbon source. The dissolved carbon atoms then move through the molten metal, driven by a temperature gradient, towards the slightly cooler diamond seed crystal.
- Growth: The carbon atoms then precipitate onto the diamond seed, crystallizing layer by layer and accurately replicating the seed’s diamond structure. The seed itself does not “grow”. Rather, it acts as a nucleation point or platform for the new diamond material to form upon.
- Cooling and Retrieval: The system is then cooled slowly over a period of time. This can range from a few days to several weeks, depending on the size and quality of the diamond. The pressure is released gradually. Then, the newly formed lab-grown diamond is extracted from the capsule, cleaned of any residual flux, and prepared for cutting and polishing.
Method 2: Chemical Vapor Deposition (CVD) Synthesis
The Chemical Vapor Deposition (CVD) synthesis technique has emerged as a modern method, producing superior gem diamonds with growing popularity. This method operates under moderate heat conditions and reduced atmospheric pressure inside vacuum-based equipment. Here are the steps involved:
- Preparation: Initially, diamond seed plates that were either produced by HPHT or obtained from other CVD diamonds are cleaned. Then, they are placed onto a substrate holder inside the vacuum chamber.
- Gas Introduction and Chamber Conditions: A vacuum chamber receives an exact carbon-rich gas composition which contains methane (CH4) as the primary component together with hydrogen (H2) as the main excess component. A controlled amount of oxygen or nitrogen exists to modify growth behavior. The heating process takes place between 700°C and 1200°C.
- Plasma Generation and Carbon Dissociation: The chamber receives its energy source through microwaves while lasers and hot filaments function as alternative power sources. The gases become ionised by this energy, resulting in the formation of plasma – an extremely energetic state of matter. In the plasma environment, hydrocarbon gas molecules such as methane experience breakdown. This results in individual carbon atoms. Hydrogen functions as a selective etching agent that removes non-diamond carbon forms, including graphite, to maintain high diamond purity.
- Deposition and Growth: The carbon atoms released during the process start their descent towards the cooler diamond seed plates. They deposit onto the seed surface, where they bond with diamond structures to build new diamond layers through atomic deposition under precise control.
- Intermittent Cleaning and Continued Growth: The CVD process needs to be stopped several times. This is because the diamonds receive removal procedures, followed by polishing operations to eliminate non-diamond carbon deposits. The result? High quality diamond material which continues to grow after returning to the chamber.
- Completion and Processing: The entire CVD diamond growth process requires multiple days to several weeks. Several stones can develop at the same time. Tabular (flat) crystals reach gemstone readiness through laser cutting followed by traditional polishing after their black graphite edges are removed.
Post-Growth Treatments
High pressure high temperature and chemical vapor deposition diamonds undergo post-growth treatments including HPHT annealing. This is to enhance their colour or clarity characteristics. Labs use specialized equipment to differentiate between natural and lab-grown diamonds as they appear identical to the naked eye. However, they do show different growth patterns, trace elements, and fluorescence properties.
Having explored the fascinating science and methods behind making lab grown diamonds, you’re now equipped to make an informed choice for your next jewellery purchase. Discover the exquisite collection of engagement rings, wedding rings, and other stunning lab-grown diamond jewellery options at Vinny & Charles today.
