Laboratory grown diamonds
HPHT & CVD
The image provided by GIA contains three diamonds in rough form. Each diamond was grown by a different process. The top two diamonds from left to right are one CVD grown diamond and one Natural diamond. The lower diamond was grown using HPHT. Each one of these diamonds has their own shape, growth structure, and number of facets.
HIGH PRESSURE, HIGH TEMPERATURE
HPHT Lab Grown Diamond Process
The High Pressure, High Temperature synthesis imitates natural diamond growth by simulating the same pressure and temperature required for them to grow deep in the earth.
The chart is a Diamond (carbon) Stabiltiy Chart showing the required pressure and temperature HPHT, CVD, and Natural Diamond need to form in. You can see that the HPHT process contains a slightly greater pressure and temperature than that of the Natural Diamond growth process.
Take note that CVD is located in the Graphite region for growth. We will discuss that in CVD.
Growing with High Pressure, High Temperature
Here is a comparison of growth structures between a Natural Diamond and HPHT Lab Grown Diamond. If you were to laser cut (saw) each diamond where the dotted lines are, you would see different growth zoning layers.
The Natural Diamond (first column) is essentially a cubic layer of expansion from one singular point. Similar to the rings of a tree, but in a cubical aspect. It lends itself to an Octahedron shape. There are eight total sides. Imagine two four sided pyramids attached at their bases. If you cut it in half, you would see the squared layers.
The HPHT Lab Grown Diamond contains fourteen sides. It is a squatty faceted cube known as a Cuboctahedron. Growth begins at the seed crystal (seen above) and expands out, and upwards into sections. Slicing it in half will show you the four main quadrants and the surrounding sections.
Therefore, a large distinguishing characteristic between a Natural Diamond and this HPHT Diamond are their growth structures.
The image to the left shows HPHT Lab Grown Diamond in its rough form. From here, the lab grown diamond is manufactured (cut) further into a popular shape the allows for maximum light return.
Chemical Vapor Deposition
CVD Lab Grown Diamond Process
The CVD Lab Grown Diamond method involves diamond growth in temperatures of 700–1300°C, but pressures of less than 1 GPa within a vacuum chamber. This is in the Graphite region, where carbon cannot crystalize into Diamond. Instead of using pressure, CVD involves a vaccuum; the opposite. A plasma energy source breaks apart gas molecules; releasing carbon atoms. These carbon atoms migrate downward toward the substrate; where they bond and become diamond. CVD Lab Grown Diamond crystals are cubic in shape because they are grown on (100) orientation diamond substrate. The finished CVD diamond tablets are referred to as “As-Grown”.
A CVD Lab Grown Diamond contains numerous, tight-knit, microscopic flat vertical layers. This unique upward growth striae is characteristic of Chemical Vapor Depostion. Close identification using gemological instruments can locate these growth striations. Remember, a Natural Diamond grows in cubic layers. These striations are also a great way to tell them apart from HPHT Lab Grown Diamonds.
CVD Color Treatment
Over half the CVD Diamonds grown are comprised of a light brown color. The High Pressure, High Temperature process is also used to remove the brown color in a CVD grown diamond. This is a permanent process. The diamond remains colorless.
In the end, whether you choose a CVD Lab Grown Diamond, HPHT Lab Grown Diamond, or a Natural Diamond, there are a few things they all have in common. All three of them are a Diamond. They all lend themselves to beauty, and are all given with love. However, a Natural Diamond's rarity will always be inescapable.