As the chemical and physical properties of natural and lab-grown diamond crystals are identical, when a gem diamond is faceted, its optical properties will also be indistinguishable. Therefore, it is impossible to tell the difference between the two with the naked eye, using a 10x loupe, or even a microscope. Lab-grown diamonds will also test as diamonds using a conventional diamond tester.

The only way to differentiate between them is to use a specialist machine that will perform various tests on the diamond and analyse its growth patterns. The machine will be able to determine whether the crystal was grown organically within the Earth over millions of years, or whether it was created under controlled factory conditions in a matter of weeks.

HPHT diamonds are characterised by distinguishing internal graining, uneven colour distribution, metallic flux inclusions, unusual fluorescence colours and patterns.

Some of the differentiating features of CVD diamonds are occasional dark pinpoint inclusions, banded strain patterns, unusual fluorescence colours and patterns.

The two different types of lab-grown diamonds are distinguished by the different methods by which they are grown.

The first is called HPHT and stands for High Pressure, High Temperature, the idea being to emulate the conditions in which natural diamonds are formed. This is the original method of creating synthetic diamonds, and it dates back to the 1950s when General Electric succeeded in making diamonds, but only of industrial grade. The procedure was perfected and eventually led to the creation of the first gem-quality crystal in 1971. Since then, with advancements in technology, this technique has become a viable method of manufacture on a vast scale.

The process works by placing a seed diamond in a specially designed chamber with internal metal presses built to withstand immense pressure and temperature. An additional pure carbon substance, such as graphite, is then introduced and dissolved in a molten flux consisting of metals such as cobalt, iron and nickel, which act as catalysts. These metals reduce the pressure and temperature to those ideal for diamond growth, enabling the carbon to attach itself to the cooler seed diamond and begin the crystallisation process. Over a period amounting to just weeks, a diamond crystal is formed. The shape of the crystal is usually characterised by an octahedral or cubic formation.

The CVD method is the more recent method of making diamonds. The first gem-quality crystal was produced in the 1980s, although it took many more years for the process to be made commercially viable. CVD stands for Chemical Vapour Deposition. Moderate heat and pressure are required in this technique.

A seed diamond is placed in a special chamber, and a gas such as methane (or one which contains both hydrogen and carbon) is introduced to the chamber. An energy source, commonly in the form of microwaves, is used to break down the gas, and the carbon molecules are attracted to the cooler seed diamond where they attach and crystallise. Every few days, the crystals are removed from the chamber so any non-diamond carbon can be removed from the surface, before they are replaced to continue the growing process, which can take days to a few weeks. It is common for these tabular crystals to form with rough graphite outer edges. In the CVD method, multiple crystals are grown in the same chamber simultaneously.

The CVD method uses less pressure and less heat than the HPHT method, and is recognised as the greener option. However, the fast growth of the crystals can result in internal spotty marks, and they also tend to have brownish undertones, so they often undergo HPHT treatment to improve their colour. The HPHT method is more costly than CVD, as it requires far greater pressure and temperatures for diamond crystals to form. However, the crystals produced are usually of a very high standard, particularly in regard to colour, and therefore, it is currently considered to be the superior process.

Both methods are continually evolving, embracing new technologies and ultimately improving.

In addition, lab-grown diamonds also present a more sustainable alternative to mined diamonds. Although the mining of natural diamonds has improved, and efforts are now made to protect or repair the landscape, the nature of digging deep open pits into the Earth has had a detrimental impact on the environment. Combined with the use of heavy industrial mining equipment, these two factors contribute to the cost of mining natural diamonds.

Lab-grown diamonds provide a more environmentally friendly alternative, with limited impact on flora and fauna. They are promoted as being more ecologically sustainable, particularly with the use of renewable energy, which helps offset the high pressure and temperature requirements for manufacturing. This is especially relevant in the production of CVD diamonds, with some factories aiming to become 100% sustainable in the future.

The world of natural diamonds has received bad press over the years, with terrible accounts of corruption, particularly in some Central and Western African countries, where the profits of diamond sales were used to finance conflicts that undermine legitimate governments.

This type of activity is portrayed in the 2006 film Blood Diamond, starring Leonardo DiCaprio. In 2003, the Kimberly Process was established, which was designed to eliminate the trade of conflict diamonds. This has led to a dramatic decline in conflict diamonds finding their way onto the market, but lab-grown diamonds offer a 100% guarantee of ethical origin.