Pearls have a way of dividing opinion like few other gems. Some people picture the uniform, glassy strand worn with evening wear; others picture something rougher, warmer and altogether more modern. Understanding what you are actually looking at — a natural pearl or a cultured one — is the first step to buying well, caring properly and styling the pieces you own with real confidence.

What Makes a Pearl "Natural"?

A natural pearl begins with an accident. A parasite, a fragment of shell or a piece of grit lodges in the soft mantle tissue of an oyster or mussel, and the mollusc responds as it always does to irritation: it coats the intruder in layer upon layer of nacre, the same iridescent material that lines the inside of its shell. Nobody helps and nobody intervenes. The pearl grows where it grows, for as long as the mollusc lives, and those densely packed layers build the deep, glowing lustre that natural pearls are famous for.

That word "accident" explains everything about their rarity. In wild shell populations, a gem-quality natural pearl turns up in perhaps one in many thousands of shells, and most of those are small, dull or misshapen. The historic pearling grounds of the Persian Gulf, the Red Sea and the Gulf of Mannar were fished for centuries to supply a handful of fine pearls a year.

Today, most natural pearls you will encounter are antique. Think of the tiny seed pearls set into Victorian brooches, the small button pearls in Edwardian pendants or the occasional heirloom strand that has been restrung more times than anyone can remember. Genuine natural pearls of any size are collector's pieces, and they are priced accordingly.

How Cultured Pearls Are Grown

Cultured pearls are still real pearls, formed by the same molluscs in the same way. The difference is that a farmer starts the process deliberately, inserting a small piece of mantle tissue and, in most cases, a round bead of mother-of-pearl shell as a nucleus. The mollusc then does what it would do anyway: it wraps the nucleus in nacre. What was a lottery becomes a harvest.

• Akoya pearls come from small saltwater oysters, usually with a bead nucleus, and take roughly one to three years to grow. They are prized for their sharp, mirror-like lustre and near-perfect roundness.
• South Sea and Tahitian pearls grow in much larger oysters over two to four years or more. The nacre is thicker, the sizes larger and the colours range from creamy white and gold to deep peacock greens and charcoals.
• Freshwater pearls are grown in mussels, often with tissue only and no bead, which is why so many of them are baroque — irregular, rippled and full of character. They are the most affordable and the most versatile for everyday wear.

The practical upshot is availability. Cultured pearls can be produced in reliable shapes, sizes and colours, which is why a good strand can be bought for the price of a nice pair of boots rather than the price of a house.

Telling Them Apart

Size alone tells you very little. A large pearl is far more likely to be cultured simply because large natural pearls barely reach the market, but the only certain test is scientific. A radiograph — an X-ray — shows the internal structure clearly: a natural pearl has concentric growth rings throughout, while a bead-nucleated cultured pearl shows a distinct central nucleus with a relatively thin outer layer of nacre.

A few practical points are worth knowing when you are shopping:

• Lustre and nacre thickness matter more than size. Thin nacre can flake or wear through at the drill hole, revealing the dull bead beneath.
• Shape is a clue, not a verdict. Baroque pearls can be natural or cultured; round pearls of significant size are almost always cultured.
• Paperwork is essential. Any pearl sold as natural should come with a report from an independent gem laboratory.
• Ask directly. A reputable seller will tell you plainly whether a pearl is natural or cultured, and will not mind you asking twice.

Caring for Pearl Jewellery

Pearl is soft — around 2.5 to 4.5 on the Mohs scale — and nacre is sensitive to acid, alcohol and abrasion. Perfume, hairspray, sunscreen and even perspiration will dull the surface over time.

• Last on, first off. Put pearls on after makeup and scent have dried, and take them off before you clean the house or go to bed.
• Wipe after every wear with a soft, slightly damp cloth, then let them dry flat before storing.
• Store separately in a soft pouch or a lined compartment, never loose in a box with metal or harder stones.
• Restring regularly — every year or two for a strand you wear often. Knotting between pearls stops you losing them all if the thread snaps.
• Skip the gadgets. No ultrasonic cleaners, no steam, no jewellery dip. A mild soap in lukewarm water is as harsh as pearls should ever get.

Rustic-Inspired Styling

Baroque and freshwater pearls suit a relaxed, earthy aesthetic beautifully, precisely because they are not perfectly uniform. A strand of irregular cream pearls looks wonderful with raw linen, oatmeal knitwear and faded denim. Try a single large baroque pearl on a waxed cotton cord, or layer fine pearl strands with oxidised silver and brass for a collected, lived-in look.

Mixing pearls with wood, leather, shell or hammered copper softens their formality. Choose warmer tones — champagne, cream, pale pink, soft grey — rather than icy white if you want the piece to feel worn-in rather than reserved. And do not save them for best. Pearls gain their glow from being worn, and a rustic setting gives them somewhere far more interesting to live.