How to Recognise a Real Pearl: Natural, Cultured, Glass or Plastic
Natural pearl, cultured pearl, freshwater pearl, pearlescent glass bead: how to tell them apart, the tooth test, and what only a laboratory can tell you.
Key points
| Nature | nacre (aragonite and conchiolin) secreted by a mollusc |
|---|---|
| Hardness (Mohs) | about 2.5 to 4.5: soft |
| Density | about 2.6 to 2.85 |
| Cases to tell apart | natural pearl, cultured pearl, shell bead, glass or plastic imitation |
| Types of culture | Akoya, South Sea, Tahiti, freshwater (mostly China) |
| Simplest test | a real or cultured pearl catches slightly on the edge of a tooth; an imitation slides off |
| Common treatments | bleaching, dyeing, polishing; black or vivid shades are often coloured |
| Fragility | sensitive to acids, perfume, sweat, knocks and dryness |
Natural, cultured, imitation: three different things
A pearl is formed by a mollusc that deposits nacre around a foreign body or an irritant. Nacre is made of platelets of aragonite (a form of calcium carbonate) bound together by an organic material, conchiolin.
- Natural pearl: formed without human intervention. Almost impossible to find today outside antique pieces; very rare and very expensive.
- Cultured pearl: formed in a farmed mollusc after a nucleus (a fragment of shell) or tissue has been grafted into it. It is a real pearl and makes up the vast majority of the market today. The process was developed in Japan at the beginning of the 20th century (Mise, Nishikawa, Mikimoto).
- Freshwater pearl: grown in freshwater mussels, today mostly in China, most of them without a nucleus.
- Shell bead or “mother-of-pearl”: a bead cut from a shell, sometimes coated with a pearlescent varnish.
- Imitation pearl: a glass or plastic bead coated with a pearlescent layer (pearl essence, a solution containing fish scales, or paint).
A cultured pearl is therefore not “fake”. An imitation pearl is an honest costume jewel when it is sold for what it is.
Warning signs
| Sign | Natural or cultured pearl | Imitation |
|---|---|---|
| Lustre | Deep glow, with iridescent shimmer (orient) that seems to come from within | Uniform surface shine, often too perfect |
| Surface | Fine irregularities, tiny growth defects | Perfectly smooth and even |
| Shape and size | Slight variations from one pearl to the next | All identical, round and flawless |
| Drill hole | Nacre in layers right up to the edge, uniform colour | Coating that flakes, white glass or plastic core visible, irregular edge of the coating |
| By touch | Cool, slightly grainy | Plastic: lukewarm and light; glass: very smooth |
| Weight | Heavier than plastic | Plastic: light; glass: heavy |
Simple and safe tests
- The tooth test. After checking that the pearl is clean, rub it very lightly against the edge of a front tooth, without biting. Nacre, made of platelets, catches and feels slightly gritty. An imitation slides off, perfectly smooth. Only do this with pearls that belong to you, and gently.
- Look at the drill hole under a magnifier: look for a flaking coating and a glass or plastic core beneath it.
- Rub two pearls against each other: nacre feels the same slightly grainy.
- Compare the pearls on a strand: variations in shape and colour for cultured pearls, perfect sameness for imitations.
- Weigh and touch: plastic is light and warms up quickly.
- Read the description: “cultured pearl”, “freshwater pearl”, “glass pearl”, “shell pearl”.
Use no vinegar, no acid and no flame: nacre is calcium carbonate, which acids dissolve, and heat dulls it.
What these tests cannot prove
No home test can tell a natural pearl from a cultured pearl: only an X-ray in a laboratory can, since a natural pearl shows concentric growth rings, whereas a cultured pearl with a nucleus shows a solid core. The tooth test also cannot identify a varnished shell bead or a dyed pearl.
Dyeing is common: most black, grey, blue or vividly coloured pearls are coloured or treated, although Tahitian pearls have a genuinely natural range (silver, grey, green, bronze-black). Bleaching and polishing are common. French regulations distinguish pearl, cultured pearl and imitation, and require significant treatments to be disclosed. For a valuable piece (a strand of South Sea or Tahitian pearls, an antique piece of jewellery), ask for a certificate from a gemmological laboratory.
Useful questions to ask the seller
Ask: are these cultured pearls, freshwater or glass? Are they dyed or bleached? What is the size and quality of the nacre? Is the thread knotted between each pearl (a sign of care)? A knot between the pearls prevents losing them all if the thread breaks, and often reveals a carefully made necklace.
For Tahitian and South Sea pearls, ask about the origin and the accompanying documents. An old natural pearl of high value should only be bought with a certificate from a gemmological laboratory.
Care and buying
Pearls are soft and sensitive: put them on last, after perfume and hairspray, wipe them with a soft, slightly damp cloth after wearing, and store them flat in a soft cloth, away from other jewellery. The thread of a necklace should be restrung regularly.
Our pearl page covers history and symbolism; the cultured or imitation pearl page compares the products. Our product sheets state the nature of each piece: see our commitments.
Frequently asked questions
How can you tell if a pearl is real?
Rub it very lightly against the edge of a tooth: nacre catches, an imitation slides. Also look at the drill hole for a flaking coating. To tell a natural pearl from a cultured one, a laboratory X-ray is needed.
Is a cultured pearl a real pearl?
Yes. It is formed by a mollusc, like a natural pearl, but in a farm. It is sold as a cultured pearl, which is accurate.
Are black pearls natural?
Some are natural (Tahitian pearls from the Pinctada margaritifera oyster). However, many very black or vividly coloured pearls are dyed or treated. Ask the seller.
Can I test a pearl with vinegar?
No. Nacre is calcium carbonate: vinegar dissolves it. This test damages a real pearl.
Why is my pearl turning yellow?
It absorbs sweat, cosmetics and perfume, and it dries out. Gentle care and sheltered storage help preserve it.
Also read
The meanings mentioned belong to tradition and symbolism. They are neither promises of results nor medical advice. Back to Recognizing real stones.