How Gemologists Tell Natural From Lab Grown Diamonds: The Science of Detection

Gemologists tell natural diamonds from lab grown ones with laboratory instruments, not with a loupe. They look at the diamond's type (how much nitrogen it contains), the way it fluoresces under intense ultraviolet light, the pattern its crystal grew in, and tiny spectral signatures left by its growth. Whether you are shopping in Miami or anywhere else, this is why a grading report from an independent lab matters so much.

Why can't you see the difference with your eyes?

Because there is no difference in what a diamond fundamentally is. A lab grown diamond is pure carbon in the same cubic crystal lattice as a natural one, with the same hardness, the same refractive index and the same fire. It is not a simulant like cubic zirconia or moissanite, which are different materials entirely.

What differs is the story of its growth. A natural diamond formed deep in the Earth's mantle over geological time. A lab grown diamond formed in weeks, in a press or a vacuum chamber. Each environment leaves fingerprints inside the crystal, and those fingerprints are what gemologists read. If you want the bigger picture on choosing between the two, start with my guide to natural vs lab grown diamonds in 2026.

How are lab grown diamonds made, CVD vs HPHT?

There are two main methods, and each leaves different clues.

• CVD, chemical vapor deposition. According to a review in GIA's journal Gems & Gemology by Sally Eaton-Magaña and James Shigley, CVD diamond grows layer by layer on a diamond seed plate, from a hydrocarbon gas such as methane mixed with hydrogen, at about 700 to 1,300 °C and at less than one atmosphere of pressure.
• HPHT, high pressure and high temperature. A press recreates mantle like conditions. Carbon dissolves in a molten metal solvent and crystallizes onto a seed. This is standard textbook chemistry, and it is why HPHT diamonds can contain tiny metallic inclusions from that solvent.

What does "diamond type" tell a gemologist?

Diamonds are classified by whether they contain measurable nitrogen and how that nitrogen is arranged in the crystal. Most natural diamonds contain nitrogen, which is part of why many have a faint yellow tint. Very pure, nitrogen free diamonds are called type IIa.

Popular Science, reporting on diamond identification, noted that fewer than 2 percent of natural diamonds are type IIa. The GIA review found that near colorless CVD diamonds were typically low nitrogen type IIa. So a colorless type IIa result does not prove a diamond is lab grown, but it tells the lab to look much more closely. My post on diamond color science explains how nitrogen and boron shape color.

How does ultraviolet light reveal a diamond's origin?

Under ordinary UV lamps, many diamonds glow faintly. Under the far more intense UV of an instrument called the DiamondView, the GIA review states, all diamonds, including all CVD synthetics, show some observable reaction. What matters is the color and, above all, the pattern of that glow.

• Color. The GIA review describes orange and red long wave fluorescence as extremely uncommon in natural untreated diamonds, while many pink CVD diamonds showed orange to red reactions.
• Frequency. In GIA's data, only 7 percent of near colorless CVD diamonds had measurable fluorescence under a standard long wave lamp, compared with 35 percent of natural near colorless diamonds in an earlier study, nearly all of them blue.
• Pattern. Because CVD grows in layers and HPHT grows outward in geometric sectors, the DiamondView image can show growth structures that natural diamonds do not have.

What is photoluminescence spectroscopy?

This is the lab's most precise tool. A laser excites the diamond, often at very low temperature, and a spectrometer records the light it gives back. Specific atomic defects emit light at specific wavelengths, like barcodes.

According to the GIA review, CVD diamonds can be identified by their distinctive fluorescence pattern in the DiamondView and by detecting the silicon vacancy defect with photoluminescence spectroscopy. Silicon can enter the crystal during CVD growth, so its signature is an important clue. The same review notes that visual gemological characteristics provide indicators, but not definitive proof, of CVD origin.

What else do gemologists look at?

• Strain patterns. Viewed between crossed polarizing filters, CVD diamonds often show weak, banded strain, which the GIA review lists among identification features.
• Inclusions. Metallic inclusions point to HPHT growth. Natural diamonds can contain tiny mineral crystals, such as garnet, picked up in the mantle.
• Laser inscriptions. Many graded stones carry a microscopic inscription on the girdle matching their report.

What does this mean when you buy a diamond?

It means trust the report, not the eye. Ask whether the stone has been graded by an independent laboratory and whether that report states its origin. For larger natural diamonds this is especially important.

In my own work I use natural diamonds. The Diamond Studs are yellow gold with 1.5 ct total of GIA certified natural diamonds, 0.75 ct each. The Rock on Rock Ring sets an approximately 1.5 ct natural conflict free diamond, GIA certified, on organic textured gold. The Wavy Diamond Hoop Earrings curve ethically sourced natural diamonds in 18K recycled gold around the ear.

Margaret Krinetz Fine Jewelry, handmade in Tel Aviv and shipped to Miami, makes every piece to order. I studied physics and biology, and I still find it wonderful that a laser and a spectrometer can read the birth story of a crystal.

Frequently asked questions

Can a jeweler tell a lab grown diamond by looking at it?

No. Origin is determined with laboratory instruments such as DiamondView imaging and photoluminescence spectroscopy.

Are lab grown diamonds fake?

No. They are real diamond, chemically and physically. They differ from natural diamonds in origin, rarity and price.

How long does delivery to Miami take?

Every piece is handmade to order in 4 to 6 weeks, then ships with DHL Express in 3 to 5 business days. Shipping is free on orders over $1,500.

Curious about a specific stone or a custom piece? Write to me, and I will explain exactly what you are looking at.