The manufacture of synthetic diamonds is an exacting and difficult process that requires a fair amount of specialized equipment and expertise. There are four major methods of creating synthetic diamonds, some easier than others and some requiring more specialized materials than others. By far the most practical and cost-effective method, however, is known as the High Pressure, High Temperature (HPHT) method.
Decide on a type of industrial press and purchase it. The two main types of high-pressure press that are used to create synthetic diamonds are belt presses and cubic presses. Either type of press will work well, but belt presses are probably easier to use and somewhat less expensive. Either way, however, you'll end up spending tens of thousands of dollars to purchase either type of press, depending on the scale of the press, its condition and the kind of deal you get on it.
Obtain a supply of pure carbon in the form of graphite. Not only is graphite the easiest form of pure carbon to shape and mold into your press, but it also lends itself particularly well to the synthetic diamond creation process.
Fill your industrial press with graphite, and make sure the press is properly powered and fueled. Different types of presses work differently, but the majority use hydraulics to do the work of the press. Make sure your equipment is operational and safe before proceeding.
Operate the press to create synthetic diamonds. You'll need to achieve temperatures of at least 2,732 degrees Fahrenheit and at least 5 atmospheres of pressure within the press to create high-quality diamonds. The faster you create these conditions with your press, the better the diamond quality will be.
Allow the press and materials to cool completely before opening the press and extracting your synthetic diamonds.
Items you will need
Pure carbon (in graphite form)
The purer your source of carbon, the better your eventual product will be. Make sure you are using completely pure graphite. Also, adulteration will seriously affect the diamond-creation process.
Remember that your only chance for turning a profit by making synthetic diamonds is to do so on a massive scale. To recoup the cost of the industrial press you bought, you'll need to churn out many thousands of synthetic diamonds for sale.
The machinery required to create synthetic diamonds is dangerous, as is the process. Always use due care and only operate the machinery if you're qualified to do so. Understand proper safety procedure when working with heavy machinery.