TL;DR
Pearls are the softest thing in most jewelry boxes, rating roughly 2.5 to 4.5 on the ten-point mineral hardness scale, and their surface dissolves in acid. Clean them by wiping each pearl with a soft cloth barely dampened with water after every wearing. Never soak a strand, never use an ultrasonic cleaner, and keep vinegar, lemon, ammonia, alcohol, and hairspray away from them entirely.
Why pearls are different from every other gem
A pearl is not a mineral crystal. It is layer upon layer of nacre, a substance made of calcium carbonate platelets bound together with an organic protein, built up by a living mollusk.
Two consequences follow from that.
First, nacre is soft. On the Mohs hardness scale, where diamond is 10 and window glass is around 5.5, pearls sit around 2.5 to 4.5. Ordinary household dust is harder. That is why wiping a dirty pearl with a rough cloth scratches it and why pearls stored loose against other jewelry come out dull.
Second, calcium carbonate dissolves in acid. Vinegar, lemon juice, and acidic cleaners etch the surface, and even perspiration is mildly acidic. The etching is permanent, because you cannot polish nacre back the way you can repolish a gemstone -- polishing just removes more of it.
Opal, turquoise, coral, amber, and jet share the general fragility, and several of them are porous as well. Everything in this article applies to them.
How do you clean pearls?
Lay the strand flat, wipe each pearl individually with a soft cloth barely dampened with plain water, and dry it right away with a second soft cloth. For heavier film, use a cloth dampened with water and the smallest trace of mild soap, wipe clean with a plain damp cloth, then dry. Never submerge the strand.
The routine that keeps pearls alive
1. Wipe them after every single wearing. This is the whole maintenance program. Skin oil, sweat, perfume, and hairspray are what dull pearls, and wiping while the residue is fresh takes seconds.
2. Use a soft, clean, lint-free cloth. Microfiber or a jeweler's cloth. Not a treated silver polishing cloth, which contains abrasive compound.
3. Barely damp, never wet. Water travels down the drill hole and into the silk thread, which stretches and weakens.
4. Dry immediately. Then leave the strand flat in open air until fully dry before storing.
5. Do not hang a damp strand. Wet silk stretches under the weight of the pearls, and a stretched strand knots badly and eventually breaks.
6. Store flat, in a soft pouch, on its own. Not in a plastic bag -- pearls need a little air, and sealed plastic can dry the nacre out over years.
Why do pearls lose their shine?
Dulling comes from a film of skin oil, perfume, hairspray, and cosmetics building on the nacre, sometimes with fine scratches from dust or from contact with harder jewelry. Wipe pearls after each wearing to prevent the film. Once acid has etched the surface, the damage is permanent and only a jeweler can assess it.
What will damage pearls permanently
Ultrasonic cleaners. The vibration can crack nacre, loosen glued pearls from posts, and damage the drill holes. Never.
Steam cleaners. Heat and pressure both.
Vinegar and lemon juice. They dissolve the calcium carbonate that pearls are made of.
Ammonia and ammonia-based cleaners. Attacks nacre and the protein binding it.
Rubbing alcohol. Dries and dulls the surface, and can damage the glue in stud settings.
Bleach and any household cleaner. No exceptions. And never mix cleaning products together in one container in any case.
Hairspray, perfume, and lotion applied while wearing them. These are the most common cause of dull pearls by a wide margin.
Hot water and dishwashers. Obvious, but people forget a ring is on.
Storing them with other jewelry. A diamond ring or a metal chain will scratch pearls in a drawer.
Harder stones tolerate a soapy soak that would ruin a pearl, as described in how to clean gold jewelry at home safely.
Last on, first off
Jewelers repeat this rule because it works.
Put pearls on after hair products, perfume, sunscreen, and lotion have fully dried. Take them off before you undress, before you exercise, and before you wash your hands.
Pearl earrings and rings take more abuse than necklaces because they meet hands, hair products, and door frames. A pearl ring worn daily will show wear in a few years no matter what.
Wearing pearls regularly is actually good for them, within reason. Skin moisture in modest amounts keeps nacre from drying out, which is one reason strands left in a safe for decades sometimes look chalky.
But sweat is acidic, so a wipe after wearing is what makes the difference. The general habit of wiping something down before storing it runs through cleaning the personal items you use every day.
Restringing and knots
A traditional pearl strand is strung on silk with a knot between each pearl. The knots stop pearls from rubbing against each other and mean that a broken strand loses one pearl, not all of them.
Silk stretches and weakens with wear, sweat, and any exposure to water. A strand worn often should be restrung roughly every year or two, and one worn occasionally every few years.
Signs it is due: visible gaps between the knots and the pearls, a strand that feels longer than it used to, discolored or fuzzy thread near the clasp, or knots that have loosened.
Restringing is inexpensive and a jeweler will also check the clasp, which is the part that usually fails first. A strand that breaks in public loses pearls permanently.
Source: Gemological Institute of America consumer care guidance for pearls
Faux pearls and coated beads
Imitation pearls are glass, plastic, or shell beads with a coating meant to mimic nacre.
That coating is thinner and more fragile than real nacre. It flakes, chips at the drill hole, and clouds. Water and alcohol both attack the coating and the glue holding beads on posts.
Wipe them dry, or with a barely damp cloth, and dry immediately. Do not soak them, ever. The rest of the plated and coated jewelry rules apply, and they are in how to clean costume jewelry without ruining it.
If pearls are set in silver that has tarnished, the situation is awkward, because the usual silver treatments are all unsafe for pearls. Clean around the pearls carefully with a cloth, or hand the piece to a jeweler. Do not use dips or the foil method described in how to clean tarnished silver jewelry.
FAQ
Can you clean pearls with soap and water?
Only with the greatest care. Use a soft cloth barely dampened with water and the smallest trace of mild soap, wipe each pearl, then wipe again with a plain damp cloth and dry immediately. Never submerge a strand, because water weakens the silk thread and travels into the drill holes.
Can pearls go in an ultrasonic cleaner?
Never. Ultrasonic vibration can crack the layered nacre, loosen pearls glued to earring posts, and damage the drill holes. Steam cleaners are equally unsafe. Pearls are cleaned by hand with a soft cloth, and anything beyond that belongs with a jeweler.
Does vinegar damage pearls?
Yes, permanently. Pearls are largely calcium carbonate, which dissolves in acid, so vinegar and lemon juice etch the surface and leave it pitted and dull. The damage cannot be polished out, because polishing nacre only removes more of it. Keep all acidic cleaners away from pearls.
How often should pearls be restrung?
Roughly every one to two years for a strand worn often, and every few years for occasional wear. Silk stretches and weakens with sweat and handling. Restring sooner if you see gaps between the knots and the pearls, discolored thread near the clasp, or knots that have loosened.
Why do pearls turn yellow?
Yellowing usually comes from accumulated skin oil, cosmetics, and hair products absorbed over years, and sometimes from nacre drying out in long airtight storage. Wiping after each wearing prevents most of it. Once yellowing is set into the nacre it cannot be reversed at home, and a jeweler should assess it.
How should you store a pearl necklace?
Flat, in a soft cloth pouch, on its own so nothing harder can scratch it. Do not hang a strand for long periods, since the weight stretches the silk, and do not seal pearls in airtight plastic for years, which can dry the nacre. Keep them out of the bathroom.
Delicate things last longer in a home where dust is under control. If you would rather hand that job off, get a quote or read more about house cleaning services.