A Visual Guide to the Lab Grown Diamond Manufacturing Process: What Each Stage Looks Like

Lab grown diamonds are made through one of two processes: High Pressure High Temperature (HPHT), which replicates the crushing conditions inside the Earth’s mantle, or Chemical Vapor Deposition (CVD), which builds a diamond carbon atom by carbon atom inside a vacuum chamber. Both methods start with a tiny diamond seed and end with a chemically identical stone that passes the same gemological tests as a mined diamond.

The difference between the two is physics: HPHT squeezes, CVD deposits. But both share the same sequence of visible, documentable stages, and understanding what each stage actually looks like helps you read a grading report, compare stones, and know what you are buying. Here is that sequence, from seed to certified gem.

What does the diamond seed look like, and why does it matter?

The seed is the part most people never picture. It is a thin slice of existing diamond, typically 1 to 3 mm across, with a polished flat surface that serves as the template for new crystal growth. At this stage, the material looks like a small, faintly translucent chip of glass. It has no sparkle yet because it has not been faceted, but under magnification you can see the crystalline surface that will guide every carbon atom deposited on top of it.

Seed orientation matters more than most buyers realize. The angle of the polished surface determines the shape the new crystal will grow into. A seed cut along the (100) plane tends to produce a blocky, cube-like rough, while (111) orientation produces a more octahedral form. Manufacturers keep inventories of seeds matched to their target sizes and shapes, so this quiet first step actually sets the ceiling for what the finished diamond can become.

What does the HPHT growth chamber look like during production?

Visually, an HPHT press is not subtle. The machine is a large, industrial-looking apparatus, either a belt press with two opposing anvils or a cubic press with six anvils arranged around a central cell. The growth capsule itself is small: it holds the seed at the bottom, a metal catalyst (iron, nickel, or cobalt are common) in the middle layer, and a carbon source such as graphite at the top.

Once the press seals and the hydraulic system engages, conditions inside reach roughly 5 to 6 GPa of pressure and temperatures between 1,300 and 1,600°C. The metal catalyst melts, the graphite dissolves into it, and carbon migrates through the molten flux toward the cooler seed, where it crystallizes layer by layer. This migration takes days to weeks. From outside the press, nothing dramatic is visible: just a sealed metal machine running at temperature. The reveal comes only when the chamber opens and the rough crystal is extracted.

What does a lab grown rough diamond look like after extraction?

This is the stage that surprises most people. Fresh from the HPHT chamber or CVD reactor, the rough diamond does not look like jewelry. It looks more like a pale, semi-opaque pebble with a greasy or glassy surface. HPHT crystals typically show both cubic and octahedral faces, giving them a blocky, multi-sided shape. CVD crystals grow in flat, plate-like layers and lack octahedral faces entirely, so they look squarish and almost stratified.

Color at this stage is unpredictable until the chamber opens. A stone that grew under slightly nitrogen-rich conditions may come out with a yellowish or brownish tint. CVD diamonds often exit the reactor with a grayish or brownish cast, which is why many then go through an HPHT annealing step: the already-formed stone is placed back into a high-pressure, high-temperature environment, which reorganizes defects at the atomic level and permanently improves the color. Nothing is added to the diamond; the lattice is simply restructured. After annealing, the same stone may shift from a near-brown to a near-colorless appearance.

Lab-grown rough stones tend to have more uniform shapes and fewer random inclusions than mined rough, because the growth environment is controlled rather than geological. But they are not automatically flawless. Any instability in chamber conditions during growth can introduce inclusions or halt crystal development entirely.

What does the cutting and polishing stage look like?

Cutting is where the rough pebble becomes recognizable as a diamond. A gem planner first studies the rough under magnification, mapping inclusions and plotting the cut that will produce the best combination of size, clarity, and light performance. Because only diamond can cut diamond, the tools used are diamond-tipped blades and lapping wheels coated with diamond powder.

The process moves through several steps: bruting (shaping the girdle by spinning two diamonds against each other), blocking (placing the first major facets), and then brillianteering (adding the remaining facets that create the finished optical pattern). A poorly executed cut can waste 20 to 30 percent of a rough stone’s potential value, so this stage requires as much skill as the growth process itself.

After cutting, the stone goes to polishing on a rotating iron wheel charged with diamond powder. The polished surface is what allows light to enter, reflect internally, and exit as the brilliance and fire you see in a finished stone. At this point, a CVD and an HPHT diamond of the same grade are visually indistinguishable from each other and from a mined diamond.

The Growth Method Determines the Finished Stone

The manufacturing process ends at certification, not at polishing. An independent grading lab, most commonly IGI for lab grown stones, evaluates the finished diamond on the 4Cs: carat weight, color on the D-to-Z scale, clarity at 10x magnification, and cut. Multiple gemologists assess each stone independently. The final report explicitly states the growth method, CVD or HPHT, and discloses any post-growth treatment such as annealing.

The last physical step is the laser inscription. A microscopic beam etches the IGI report number and the words “LAB GROWN” onto the diamond’s girdle, the narrow band around its widest point. This inscription is invisible to the naked eye but readable under a 10x loupe, and it ties the physical stone permanently to its paper record. It is the detail that makes certification traceable rather than just decorative.

Every lab grown diamond at Ouros Jewels carries IGI certification, so each stage of this process, from growth method to post-growth treatment to final grades, is documented before a stone is set into jewelry. If you want to see that documentation applied to a finished piece, the customized lab grown diamond stud is a good starting point: you choose the stone, and the IGI report travels with it.

Frequently Asked Questions

How long does it take to grow a lab grown diamond from seed to rough stone?

Growth time varies by method and target size. HPHT crystals typically form over several days to a few weeks inside the press. CVD diamonds grow in thin layers over three to four weeks, with the reactor paused periodically to polish the top surface and remove non-diamond carbon before growth resumes. Larger stones take longer in both methods.

Can you tell a CVD diamond from an HPHT diamond just by looking at it once it is polished?

No. Once cut and polished to the same grade, both types are visually identical to each other and to a mined diamond. Distinguishing them requires advanced spectroscopic equipment available only in gemological laboratories. The IGI grading report will state which method was used, so you do not need to guess.

Why do some lab grown diamonds go through a second HPHT treatment after CVD growth?

CVD diamonds often exit the reactor with a brownish or grayish tint caused by structural defects that absorbed light unevenly. A post-growth HPHT annealing step applies heat and pressure to reorganize those defects at the atomic level, shifting the color toward colorless or near-colorless without adding any new material to the stone.

Does the seed crystal affect the quality of the finished lab grown diamond?

Yes, in a meaningful way. The seed’s crystal orientation determines the growth morphology of the new diamond, and any defects in the seed can propagate into the growing crystal. Manufacturers select seeds carefully and match them to target size ranges. A high-quality seed is one reason lab grown diamonds from reputable producers tend to have consistent clarity across a batch.

What is the laser inscription on a lab grown diamond’s girdle, and do I need it?

The inscription is a microscopic alphanumeric code etched by a fine laser beam onto the girdle of the diamond. It includes the IGI report number and typically the words “LAB GROWN.” It links the physical stone to its grading certificate, making it easy to verify the stone’s identity under a 10x loupe. You do not need to read it yourself, but its presence means the stone and the certificate are permanently connected.