How to identify real Rubies vs lab-grown ones: Expert identification guide

Rubies are one of the most imitated gemstones. Today’s lab-grown rubies are chemically and physically the same as natural ruby. That makes identification tricky. The good news: a careful look with simple tools can often separate natural from lab-grown. This guide shows you what to look for, why it matters, and where you’ll need a professional lab.

What “real” means: natural vs lab-grown ruby

Ruby is corundum colored red by chromium (Cr). Natural rubies form in the earth over millions of years. Lab-grown rubies crystallize in a factory in weeks to months. Both are aluminum oxide with the same crystal structure. Both are hard (Mohs 9). Both can be very clean and bright red.

So what’s the difference? Rarity, growth features, and inclusions. Natural rubies show features from geologic growth and stress. Lab-grown rubies show features from the manufacturing method. Those growth markers are the key to identification.

Fast clues you can check in minutes

These observations are quick. Alone they are not final proof, but together they point you in the right direction.

• Price and story. Fine natural ruby is rare and expensive. If a vivid, clean, 2-carat “Burma-like” ruby is priced like a small garnet, assume lab-grown. Always ask where it was sourced and whether it is lab-grown or treated. Why: rarity drives natural prices; labs can make clean stones cheaply.
• Cut and color uniformity. Lab-grown rubies are often very evenly colored and very clean. Natural rubies often show slight color zoning, small inclusions, and a more “textured” look under magnification. Why: factory growth is controlled; nature is not.
• Avoid scratch tests. Ruby can scratch glass, but so can many cheaper materials. You could also chip your stone. Why: it proves hardness, not origin, and risks damage.

Use a loupe: inclusions tell the growth story

A 10x loupe or a basic microscope is the most useful tool. Take your time. Use side lighting and rotate the stone slowly.

Natural ruby: what you’re likely to see

• Rutile silk. Fine, intersecting needles at 60°/120°, sometimes forming a soft haze. In star rubies, silk creates the star. Why: rutile crystallizes within natural corundum during slow cooling.
• Fingerprint inclusions. Healed fractures that look like tiny branching “fingerprints” or “feathers.” Why: stress cracks partially healed over geologic time.
• Mineral crystals and halos. Small crystals (e.g., zircon, spinel) sometimes with “discoid” stress halos around them. Why: foreign crystals trapped during natural growth.
• Angular growth zoning. Straight, angular or hexagonal color bands. Best seen in immersion (stone in water or baby oil) with backlighting. Why: corundum grows in a hexagonal crystal system.

Lab-grown ruby: features vary by method

• Flame-fusion (Verneuil). Look for curved color bands or curved striae—graceful arcs that follow the contour of the boule. You may also see gas bubbles, often spherical, sometimes aligned along the curved bands. Why: the molten droplet builds in layers that arc as the boule forms.
• Flux-grown. Expect flux “fingerprints”—soft, low-relief, puddle-like veils that don’t have the crisp, angular look of natural fingerprints. You may see wispy flux veils and occasional tiny reflective metallic platelets from the crucible. Why: ruby grows from a molten flux that can seep into cavities and solidify.
• Hydrothermal. Look for chevron or zig-zag growth zoning and two-phase inclusions (tiny cavities with liquid and gas). Often very clean, with no rutile silk. Why: growth from hot solutions creates distinctive zoned layers.

Tip: Not seeing rutile silk does not prove a stone is lab-grown. Many natural rubies are heated, which can dissolve silk. Look for a combination of clues.

Light-based checks you can do at home

These are supportive tests. They help build a case but rarely stand alone.

• Longwave UV (365 nm). Use a small UV flashlight in a dark room. Many natural rubies fluoresce red due to chromium. Burmese stones often glow strongly; Thai rubies, which are iron-rich, may glow weakly or not at all. Flame-fusion synthetics commonly show very strong, even red fluorescence across the whole stone. Why: chromium causes fluorescence; iron suppresses it. Factory rubies often have high chromium and low iron.
• Dichroscope. Ruby is strongly pleochroic. You should see two shades (purplish red and orangey red). That confirms corundum but not origin. Why: pleochroism is a property of the crystal, not its source.
• Chelsea-style filter. A chromium-rich ruby often appears red. Both natural and synthetic with chromium will pass this test. Why: the filter isolates red—useful to separate garnet or glass, not natural vs lab-grown ruby.

Instrument tests a jeweler or gemologist uses

When a loupe isn’t enough, simple instruments nail down species and reveal growth.

• Refractometer. Ruby’s RI is about 1.762–1.770 with birefringence near 0.008. This distinguishes ruby from glass or spinel, but not natural vs lab-grown. Why: chemistry and structure are the same in both origins.
• Desk spectroscope. Look for chromium lines near 693–694 nm and absorption in the green. Not diagnostic for origin. Why: both origins with chromium show similar spectra.
• Immersion microscopy. Placing the stone in a liquid close to its RI reveals growth zoning clearly. Curved zoning points to flame-fusion; straight/angular zoning supports natural. Why: immersion reduces surface glare so you can read internal structure.
• Advanced lab testing. Raman/FTIR can detect flux residues or fillers. Trace-element analysis (e.g., LA-ICP-MS) can show patterns typical of natural deposits vs lab-grown. Why: growth environment leaves a chemical fingerprint.

Treatments that complicate the picture

Origin and treatment are separate questions. A natural ruby can be heavily treated; a lab-grown ruby can be untreated. Know these common treatments:

• Heat treatment. Common in natural ruby. It can dissolve rutile silk into “snowball” clouds or leave partially resorbed silk. Why it matters: heat can remove the very inclusions you rely on, making natural stones look cleaner.
• Lead-glass filling. Fracture-filled rubies show a blue/purple “flash effect” at certain angles and tiny gas bubbles confined to fracture lines. The filled areas can look glassy and reflective in a mosaic pattern. Why it matters: the stone is natural, but durability and value drop sharply.
• Diffusion. Surface diffusion can add or enhance color in corundum. It’s less common in ruby than sapphire but exists. Look for stronger color at the surface or along facet junctions under magnification. Why it matters: the color is not uniform through the stone.

Decision path: how to work through a stone

Use this sequence to build confidence before you buy or submit for a lab report.

• Step 1: Confirm it’s corundum. Check hardness clues (carefully), RI if available, and pleochroism with a dichroscope. Why: you first need to rule out lookalikes like glass, garnet, or spinel.
• Step 2: Loupe the inclusions. Look for rutile silk, healed fingerprints, crystals, and angular zoning (natural) versus curved striae and gas bubbles (flame-fusion), or flux veils/metallic platelets (flux-grown). Why: inclusions are the clearest origin markers.
• Step 3: Use UV. Note fluorescence strength and evenness. Extremely strong, uniform red coupled with curved zoning increases the odds of flame-fusion. Why: it supports, but doesn’t decide, the call.
• Step 4: Check for treatments. Scan for flash effects and filled fractures, and note any surface-concentrated color. Why: treatment alters value and can confuse origin clues.
• Step 5: If value is high, get a lab report. Ask for a report stating natural vs synthetic and any treatments. Why: only a lab can make a definitive call on borderline cases.

Special case: star rubies

Asterism (the star) comes from dense rutile silk aligned along crystal axes.

• Natural star ruby. The star’s rays may be slightly soft, uneven, or discontinuous. The body color can be slightly hazy due to abundant silk. Why: natural silk is rarely perfectly uniform.
• Synthetic star ruby. Often shows a very sharp, bright, perfectly centered star that glides smoothly over the surface. Under magnification, you may still find curved striae or other synthetic markers. Why: lab growth can load the crystal with perfectly aligned rutile.

Red flags and myths to ignore

• “It scratches glass, so it’s real.” Many cheap materials do. It doesn’t prove origin and risks damage.
• “If it’s very red, it’s fake.” Fine natural rubies can be intensely red. The issue is combining color with the right inclusions and price context.
• “UV fluorescence proves natural.” It doesn’t. Flame-fusion rubies often glow more strongly than natural stones.

Buying tips to avoid surprises

• Ask direct questions. “Is it natural or lab-grown?” “Is it treated?” “What treatments?” You want clear, written answers on the receipt.
• Prefer sellers who offer lab reports for higher-value stones and have a return policy.
• Match the price to the story. If the stone is clean, vivid, and large, but priced low without a report, assume lab-grown until proven otherwise.
• Use your loupe before you love it. A two-minute inclusion check prevents costly mistakes.

Quick reference: natural vs lab-grown—what weighs most

• Most persuasive for lab-grown: curved growth lines, strings of gas bubbles, flux veils/metallic platelets, flawless clarity with “too good to be true” price.
• Most persuasive for natural: rutile silk (especially aligned in three directions), angular/hexagonal color zoning, natural fingerprints, mineral crystals with stress halos.
• Not decisive either way: strong red fluorescence, RI values, spectral chromium lines, pleochroism.

The bottom line: you identify a ruby by its growth story. Natural stones carry the marks of slow, messy geology—silk, fingerprints, crystals, and angular zoning. Lab-grown stones carry the marks of controlled manufacture—curved striae, gas bubbles, flux residues, or chevron zoning. Use a loupe, use light wisely, and when the stakes are high, let a lab make the final call.