An imitation pearl is a bead of something else — glass, plastic, or shell — coated with a lustrous substance to mimic nacre. Good ones are convincing at a glance and are sold honestly as fashion jewellery in vast quantities. Dishonestly, they are sold as cultured or even natural pearls, and a buyer paying a pearl price for a coated bead deserves to know.
What imitation pearls are made of
Glass beads coated with "pearl essence" — originally a suspension of fish-scale guanine crystals, now synthetic pigments in lacquer — applied in layers. The best have several coats and a soft lustre. Heavier than nacre for their size.
Plastic beads coated similarly; very light, warm to the touch, often with a mould seam.
Shell beads (mother-of-pearl cores) coated with lacquer — the "Mallorca" or "shell pearl" type. These are the most convincing because the core is shell, the weight is about right, and the coating can be thick and smooth. They are still coated beads.
Solid mother-of-pearl beads, uncoated, sold as "shell pearls". These are genuine shell — nacre, in fact, from the shell lining — but not pearls; they lack the concentric structure and usually show a flat, layered look and the sheen of cut shell.
How they are detected
The drill hole. The single most useful check. On a coated bead, the coating stops at the hole and can be seen as a distinct layer, often flaking, chipped or lifted at the edge, with the core material (glass, plastic, shell) visible beneath. On a genuine pearl the nacre continues into the hole; the edge is clean and shows nacre layers.
Surface structure. At 10× and above, nacre shows an overlapping-platelet or "fingerprint" texture — irregular, scaly ridges. A coated bead shows a smooth, uniform, sometimes slightly granular lacquer surface, occasionally with a dust particle or brush mark trapped in it.
Feel. Nacre is faintly gritty against the teeth or against another pearl because of the platelet structure; coating is smooth. This is the "tooth test", useful for coated imitations and for nothing else. The pearl tooth test.
Uniformity. Imitations in a strand tend to be identical in size, colour and lustre. Real pearls, even matched strands, vary slightly.
Weight. Glass-cored imitations are heavy; plastic-cored are light; nacre is in between (SG 2.6–2.85). Weighing a strand and comparing with the expected weight for its bead size separates the extremes.
UV. Coatings and plastic cores often fluoresce differently from nacre; some are inert where nacre glows softly.
X-ray. Shows a solid, uniform core with no nacre layering, and the coating barely registers. Conclusive, though rarely needed. X-ray of pearls.
Lustre. Nacre's lustre has depth — the "orient" from light interference in the layers. Coated beads have a surface shine that sits on top.
Half-way cases
Coated cultured pearls. Genuine pearls with a lacquer coating to improve lustre or protect thin nacre. Nacre beneath; coating detectable at the hole. A treatment, to be disclosed.
"Composite" pearls. Shell beads with a very thin layer of genuine nacre — effectively very-thin-nacre cultured pearls. The X-ray decides, and nacre thickness is stated.
What a report says
Imitation pearl (coated glass bead) or coated shell bead or mother-of-pearl bead — the material of the core and the presence of coating. A strand may be reported as a whole where all beads are alike.
Frequently asked questions
Are shell pearls real pearls?
They are shell — the same material as nacre, from the shell lining — but not pearls, which form as concentric layers around a centre within the mollusc. They should be sold as shell beads.
Can a coated bead pass the tooth test?
Well-made shell-core imitations with a textured coating occasionally feel slightly gritty. The drill hole is more reliable.
Do imitation pearls have any value?
As fashion jewellery, yes, and good ones are made with care. They have no value as pearls.
How do I check the drill hole without a microscope?
A 10× loupe and good light. Look for a layer at the rim and for a different material beneath.
Is a very perfect, very round pearl suspicious?
Fine cultured pearls are very round. Perfect uniformity across a whole strand at a low price is the warning sign, not roundness itself.