5 Things That Can Go Wrong During Lab Diamond Growth and How They Are Fixed

Lab diamond growth is not a flawless process. The five most common problems are color tinting from nitrogen or structural defects, metallic inclusions from catalyst materials, internal strain lines from uneven growth, polycrystalline contamination at crystal edges, and seed crystal defects that carry imperfections forward into the finished stone. Each has a known fix, and modern manufacturers apply them routinely before a stone reaches a grading lab.

Understanding what goes wrong during growth matters for buyers, not just producers. A stone that looks identical on paper to another may have been grown under very different conditions. The problems below are real, well-documented, and worth knowing before you buy.

What causes color tinting in lab grown diamonds, and can it be removed?

Color tinting is probably the most discussed production problem, and it shows up differently depending on the growth method.

In CVD diamonds, the issue tends to be a brownish or grayish tint that appears immediately after the stone comes out of the reactor. The cause is tiny structural defects in the crystal lattice that form during rapid layer-by-layer growth. These are not impurity atoms; they are vacancies and distortions in the carbon structure itself.

In HPHT diamonds, the culprit is almost always nitrogen. Because HPHT growth happens in an open metal environment, nitrogen can enter the crystal during formation. Even small amounts absorb blue-violet light and produce a yellow or amber tint. Early HPHT diamonds from the 2000s were almost universally yellow for this reason.

The fix for CVD tinting: a post-growth HPHT annealing treatment, typically 15 to 30 minutes in a press at high temperature and pressure. This realigns the crystal structure and permanently removes the brown or gray cast. Approximately 80% of CVD diamonds go through this step before sale, and the result is a stable, colorless stone. The 2020s saw a significant jump in D, E, and F color submissions to grading labs, largely because this treatment became more refined.

The fix for HPHT yellowing: manufacturers use nitrogen getters, aluminum and titanium additives in the catalyst that capture nitrogen before it bonds to the growing crystal. Over the past decade, producers have become far more effective at this, and consistently colorless HPHT stones are now routine rather than exceptional.

How do metallic inclusions form in lab diamonds, and what happens to them?

This problem is specific to HPHT growth. The process uses a molten metal catalyst, typically a mix of iron, nickel, and cobalt, to dissolve carbon and feed it to the growing crystal. Occasionally, tiny traces of that catalyst become physically trapped inside the lattice during growth. The result is small metallic inclusions: dark needle-like particles that can make the stone weakly magnetic.

These inclusions are visible under magnification and show up on IGI or GIA grading reports. They are one of the markers graders use to identify HPHT stones, since natural diamonds almost never capture metals during formation.

The fix: careful control of catalyst purity and growth temperature reduces the frequency of metallic inclusions considerably. Premium HPHT producers also run a post-growth purification step at very high temperatures to remove excess metallic contamination from the crystal surface. The inclusions that remain are small enough to fall within VS or VVS clarity grades in well-grown stones. For buyers, the practical implication is simple: check the clarity grade and the grading report, not just the carat weight.

Why do internal strain lines appear inside CVD diamonds, and how are they addressed?

CVD growth is a stop-and-start process by nature. Carbon deposits atom by atom onto the seed, building up in layers over two to six weeks. As the crystal grows, polycrystalline material sometimes builds up along the edges, and internal stress accumulates within the crystal body. When that stress reaches a threshold, the grower stops the reactor, lasers off the problematic layer, and restarts growth. Each of those interruptions leaves a faint ring inside the crystal: a striation.

Striations are visible under crossed polarizers as banded strain patterns. They do not affect hardness or durability, but in a poorly grown stone they can create a faint hazy or oily appearance that reduces brilliance.

The fix: slowing the growth rate is the most direct solution. High-quality jewelry-grade CVD diamonds are grown at 0.1 to 10 microns per hour, a deliberately slow pace that keeps stress from accumulating. Post-growth HPHT annealing also heals much of the remaining strain by allowing the crystal structure to relax. A stone grown slowly and then annealed will almost always outperform one grown fast and left untreated, even if both carry the same clarity grade on paper.

What goes wrong with the seed crystal, and why does it matter?

Every lab diamond starts with a seed: a thin slice of existing diamond that acts as the atomic template for new growth. The carbon atoms depositing from the gas phase (CVD) or from the molten catalyst (HPHT) align with the seed’s lattice, replicating its structure exactly. That replication is the whole point, but it also means that any defect in the seed gets copied into the new crystal.

Seeds can have faults, uneven surfaces, and varying degrees of crystallographic perfection. High-quality seeds can cost up to ten times more than lower-grade ones, which is why some producers reuse seeds past their useful life. Each additional growth run on the same seed tends to increase dislocation density in the resulting stone.

The fix: sourcing fresh, high-purity seeds and inspecting them optically before each run. Better producers use seeds from their own previous high-quality growth runs and retire them after a set number of cycles. It is an area where production discipline matters more than any single piece of equipment.

How does graphite contamination occur in CVD diamonds, and can it be corrected?

Carbon, under the wrong conditions, does not form diamond. It forms graphite. In a CVD reactor, the goal is to keep conditions precisely in the range where diamond is the stable phase. If the temperature spikes, the gas mixture shifts, or the plasma becomes uneven, carbon atoms can revert to graphite bonds instead of diamond bonds. The result is small dark graphite inclusions, sometimes described as black pinpoints, inside the finished crystal.

This is distinct from the metallic inclusions in HPHT stones. Graphite inclusions have no metallic luster and are not magnetic. They are, however, visible under magnification and can affect the clarity grade.

The fix: real-time monitoring of reactor temperature, gas balance, and plasma uniformity. Optical inspection systems check for spotty inclusions and undesirable growth patterns during and after the run. If contamination appears in an early growth layer, producers can stop the process, polish the growing surface to remove the affected material, and restart. That intervention adds time and cost, but it salvages the seed and prevents the defect from propagating through the full stone.

IGI Certification Is What Separates a Fixed Stone from a Flawed One

Every problem described above has a known solution, and the best producers apply all of them. But the buyer has no way to verify that without independent grading. An IGI certificate documents the color grade, clarity grade, and growth method, giving you a standardized record of what the stone actually is after all the post-growth treatments are done.

At Ouros Jewels, every lab grown diamond comes with IGI certification, so the grade you see reflects the finished stone, not the rough that came out of the reactor. If you want to see what that looks like in a finished piece, the Lab Grown Ring collection shows a range of certified stones across cuts and settings. The certificate does not tell you which problems occurred during growth. It tells you they were fixed well enough to matter.

Frequently Asked Questions

Does post-growth HPHT treatment make a CVD diamond less real or lower quality?

No. Post-growth HPHT annealing is a standard, disclosed step that permanently improves a CVD diamond’s color by correcting structural defects in the crystal lattice. The treatment is stable, does not affect hardness or optical properties, and is noted on IGI and GIA grading reports. The finished stone is chemically identical to an untreated one.

Can a lab diamond develop new inclusions or color changes after purchase?

No. Lab grown diamonds have the same physical and chemical stability as natural diamonds. The inclusions and color characteristics present at grading are permanent. Neither CVD nor HPHT diamonds will develop new internal flaws or shift color under normal wearing conditions, including exposure to heat from everyday jewelry repair.

Why do two lab diamonds with the same IGI clarity grade sometimes look very different?

Clarity grade captures the size and position of inclusions but does not fully describe strain patterns, graphite distribution, or the transparency of the crystal body. A VS1 stone grown slowly with a high-quality seed can look noticeably more brilliant than a VS1 grown fast with a degraded seed. Cut quality compounds this further, since a well-grown crystal can still appear dull after poor cutting.

Are metallic inclusions in HPHT diamonds a safety concern for jewelry wear?

No. The metallic particles trapped in HPHT diamonds are microscopic, fully encased in the crystal lattice, and pose no risk during normal wear. The weak magnetic response some HPHT stones show is detectable only with sensitive equipment, not by handling. The inclusions affect clarity grade and appearance under magnification, not durability or wearability.

How can a buyer tell if a lab diamond’s color tinting was properly corrected?

The most reliable indicator is the color grade on the IGI or GIA certificate. A stone that grades D through F has passed independent grading as colorless, regardless of what tinting occurred during growth. Requesting a 360-degree video of the stone before purchase also helps, since residual gray or brown tints that survived treatment are usually visible on video even when they do not show in still photos.