Ultrasonic vs Steam Cleaning: Which Stones Survive Each
A customer brought us a ring last spring with an emerald that had a white line running through it. The line was not there a month earlier. She had bought a small ultrasonic cleaner online, dropped the ring in for five minutes, and pulled out a stone with a fracture that now reached the surface and had gone pale where the oil had left it. Nothing was wrong with the machine. The emerald had a natural break inside it from the day it came out of the ground, and the cleaner found it. This is the most common avoidable damage we see.
How an ultrasonic cleaner actually works
An ultrasonic cleaner is a metal tank of water with a transducer bonded to the bottom. The transducer vibrates thousands of times per second and sends sound waves through the liquid. GIA describes these machines as generating high-frequency sound waves that travel through water or a cleaning solution, creating heat and pressure, and dislodging dirt from behind gems.
Here is the part that matters. Those sound waves create pressure changes, and in the low-pressure moments the water forms microscopic bubbles that collapse an instant later. That is cavitation, and each collapse releases a burst of energy against whatever surface is nearby. The energy does not stop there. When a bubble collapses against a stone with a break running to the outside, the force travels into that break. Jewellers call these breaks feathers, and most coloured stones have them. The cleaner pushes the two faces apart thousands of times per second, and a hairline you needed a loupe to find becomes a line you can see across the room.
How steam cleaning is different
A steam cleaner holds water in a sealed boiler and releases it through a narrow nozzle as hot vapour under pressure. There is no cavitation and no vibration. Heat softens the grease and pressure blows it away, which makes a steam jet fast on a gold chain dulled by body oil.
The risk changes shape. Heat is the danger here. GIA lists tanzanite, sunstone, moonstone, fluorite, iolite, kunzite, lapis lazuli, malachite, opal, topaz, turquoise and zircon among gems susceptible to heat and temperature changes, treated or untreated. Peridot belongs on that list too, and GIA states that rapid or uneven heat can cause it to fracture. Steam also has a failure mode ultrasonic does not: on a stone whose fractures hold oil or resin, heat drives the filler back out. GIA warns that hot steam can cause oil or unhardened resin to sweat out of fractures, leaving white lines where the filler used to be.
The method that is safe for nearly everything
Warm water, plain dish soap, a soft toothbrush. It sounds too simple to be the professional answer, and it is the professional answer. GIA calls warm soapy water the only safe way to clean opal, GIA calls it the best method for peridot, GIA calls gentle scrubbing with warm soapy water the safest way to clean emeralds, and GIA notes it is always safe for ruby.
Our bench routine: warm water, one drop of dish soap, soak five minutes, brush behind and underneath the stone, rinse with a strainer in the drain, then let the piece air dry for an hour, because trapped water under a stone leaves a mark. More on metal care in our guide to cleaning gold jewellery at home.
Stone by stone: what each method does
| Gem | Mohs hardness | Ultrasonic | Steam | Why |
|---|---|---|---|---|
| Diamond, untreated | 10 | Shop only, after inspection | Shop only | Hardest gem, and surface-reaching feathers can still open |
| Diamond, fracture-filled | 10 | No | No | Filler in the breaks can be damaged |
| Ruby and sapphire, untreated or heat-treated | 9 | Usually safe | Usually safe | Excellent toughness and no cleavage |
| Ruby, fracture-filled or dyed | 9 | No | No | Damp cloth only, the lead glass reacts to mild acids |
| Emerald | 7.5 to 8 | No | No | Fair to good toughness, and most are fracture-filled |
| Topaz | 8 | No | No | Heat-sensitive, and it has perfect cleavage |
| Peridot | 6.5 to 7 | No | No | Rapid or uneven heat can fracture it |
| Tanzanite | 6 to 7 | No | No | Heat-sensitive, poor toughness |
| Moonstone and sunstone | 6 to 6.5 | No | No | Feldspar, heat-sensitive and cleaves |
| Opal | 5 to 6.5 | No | No | Lowest toughness rating GIA gives, heat causes crazing |
| Turquoise | 5 to 6 | No | No | Porous, and heat or solvents damage treated surfaces |
| Lapis lazuli and malachite | 5 to 6 | No | No | Heat-sensitive and often wax-impregnated |
| Pearl | 2.5 | Never | Never | Soft, porous, and layered |
| Coral, amber, ivory, jet, shell cameo | Varies | Never | Never | Organic materials that the vibration separates |
| Plain gold or platinum, no stones | Metal | Yes | Yes | Nothing present that cavitation or heat can open |
The hardness column explains less than people expect. Topaz is 8 on the Mohs scale, harder than emerald, and still stays out of both machines because it has a cleavage plane and dislikes heat. Hardness measures scratch resistance. Toughness measures resistance to breaking. We cover the difference in our post on jewellery care by gemstone hardness.
The treatment question nobody asks
Whether a stone is treated changes the answer more than what the stone is. A heat-treated ruby and a lead-glass filled ruby look alike across a counter and belong in different categories. GIA rates corundum at 9 on the Mohs scale with excellent toughness and no cleavage, and says ultrasonic and steam cleaners are usually safe for untreated, heat-treated and lattice diffusion treated stones. For fracture-filled, cavity-filled or dyed rubies the guidance drops to a damp cloth, and GIA warns that even mild substances like lemon juice can cause changes in the high-lead content glass.
Emerald is the clearest case. GIA reports that some estimates put fracture-filled emeralds at 90 percent or more, using oils, resins and polymers that heat, light and chemicals can damage. If nobody told you your emerald was untreated, assume it is filled and keep it out of both machines.
GIA puts turquoise at 5 to 6 on the Mohs scale, says it should never be cleaned with steam or ultrasonic, and notes that heat or solvents can damage treated surfaces. Most turquoise sold has been stabilised with polymer. GIA also keeps star varieties out of an ultrasonic entirely.
When a professional ultrasonic is the right tool
We run ours every day, and it earns its place on two kinds of work: metal with no stones, such as a gold chain or a plain wedding band, and a sound untreated diamond in a sound setting. Nothing in either case can be opened by cavitation.
Here is the step home users skip. Before any piece goes in our tank, it goes under a 10x loupe. We look for breaks that reach the surface, chips on the girdle, movement when we tap the stone with a probe, prong tips worn thin, and the flash of colour that means a fracture holds filler. Anything with a feather reaching the surface goes into warm soapy water instead. That two-minute inspection is the whole difference between a professional clean and a gamble, and it is how most loose stones get caught before they fall.
What to do with the machine you already bought
Keep it for metal. A home ultrasonic is useful on a plain chain, a stainless watch bracelet, or eyeglass frames. Use plain water with a drop of dish soap, leave the heater off, run cycles of sixty to ninety seconds, and suspend items so nothing rattles against the tank floor. Keep out anything with a coloured stone, anything organic, anything you inherited, and anything you have not had checked. If you cannot remember whether the stone is treated, that counts as not knowing.
Rings we make and set at the shop
Every ring below was finished at our Coquitlam bench, so we know which stone sits in each one and how it should be cleaned. Ask at pickup and we will write the method down for you.
Key Takeaways
- Ultrasonic cleaners work by cavitation, microscopic bubbles collapsing against the surface, and that energy travels into any break that reaches the outside of a stone.
- Steam carries a different risk: heat. It can fracture temperature-sensitive gems and drive oil or resin out of filled emeralds.
- Warm water, one drop of dish soap and a soft toothbrush is the method GIA recommends for opal, peridot, emerald and ruby alike.
- Pearls, coral, tortoise shell, ivory, shell cameos, jet and amber must never go in an ultrasonic, and neither should fracture-filled or dyed stones.
- A professional ultrasonic is safe because somebody loupes the stone for surface-reaching fractures first, which takes two minutes and is the step home users skip.
Frequently Asked Questions
What does an ultrasonic cleaner actually do to a stone?
The machine sends high-frequency sound waves through a tank of water. Those waves create millions of tiny bubbles that form and collapse against every surface, which is how dirt behind a diamond gets knocked loose. GIA describes these machines as generating high-frequency sound waves that travel through water or a cleaning solution, creating heat and pressure. The bubbles do not choose where to release their energy. If a stone already has a break reaching the surface, that energy travels into the break and pushes it wider. A hairline you could not see without a loupe becomes a visible line, or the stone splits along it. The machine did not create the weakness. It found one already there and finished the job.
Is steam cleaning safer than ultrasonic?
They carry different risks. A steam cleaner fires hot vapour under pressure, which cuts through skin oil and polishing compound. The risk is heat, and GIA names tanzanite, sunstone, moonstone, fluorite, iolite, kunzite, lapis lazuli, malachite, opal, topaz, turquoise and zircon among gems that should stay out of an ultrasonic because they are sensitive to heat and temperature changes. Those stones dislike a steam jet for the same reason. Steam has a second problem on filled stones: on an emerald whose fractures hold oil or resin, GIA warns that hot steam can cause that filler to sweat out of the fractures, which leaves the breaks looking white and obvious. Warm soapy water and a soft brush avoid both of these failure modes, which is why it stays our default for any stone we have not inspected.
What is the safest way to clean jewellery at home?
Warm water, a drop of plain dish soap, and a soft toothbrush. That is what we use on the bench, and it is the method GIA calls the only safe way to clean opal, GIA calls the best method for peridot, and GIA calls the safest way to clean emeralds. Soak a few minutes so the soap loosens the film of hand cream and skin oil, brush behind the stone where dirt collects, rinse, and dry with a soft lint-free cloth. Put a strainer in the sink first. More than one customer has arrived holding a ring that lost a small stone down the drain during a rinse. The process takes four minutes, costs nothing, and is safe on every gem we have listed in this post.
Can I put my diamond engagement ring in an ultrasonic?
In a shop, usually yes, after somebody has looked under magnification. Diamond rates 10 on the Mohs scale according to GIA, and a clean untreated diamond in a sound setting handles an ultrasonic without trouble. Two things change that. A diamond with a feather or included crystal reaching the surface can be pushed further open by cavitation. And a lead-glass fracture-filled diamond has filler the process can damage, so GIA advises against using an ultrasonic on gemstones with surface-reaching breaks that have been filled. GIA also lists ultrasonic and steam cleaners among the harsher methods not recommended for home use. Bring the ring to us and we will loupe it first. That inspection is free and it takes two minutes.
Which stones must never go in an ultrasonic cleaner?
Start with organic materials. GIA states that pearls, coral, tortoise shell, ivory, shell cameos, jet and amber should not be put in an ultrasonic cleaner. These grew rather than crystallised, and several are held together by organic layers the vibration separates. GIA is direct about it: pearls should never be cleaned in an ultrasonic or steam cleaner, and pearl sits at 2.5 on the Mohs scale. Then add the heat-sensitive group, which GIA lists as tanzanite, sunstone, moonstone, fluorite, iolite, kunzite, lapis lazuli, malachite, opal, topaz, turquoise and zircon. Then add anything treated: fracture-filled stones, dyed stones, and gems impregnated with oil, plastic or wax. Star sapphires and star rubies stay out too, because the fine needles that create the star are breaks in the crystal by another name. When in doubt, the warm soapy water method is safe for every gem on every one of these lists.
Can an ultrasonic cleaner loosen my prongs?
Yes, and this is the damage people notice last. The vibration acts on the whole piece, so a prong already thinned by wear can shift in the tank, and a stone that was snug on Monday has a little play on Tuesday. Movement that small is silent. You will not hear a rattle or see a gap, and the stone can sit in place for weeks before it goes. Chains suffer too, because a tangled chain vibrating against a ring shank can bend a claw or open a jump ring. This is why we check settings after a clean, not only before. If you run a home machine, press each prong tip with a fingernail afterwards and watch for any shift.
Are cheap home ultrasonic cleaners different from professional ones?
The physics are the same, and that is the point people miss. A $40 tank produces the same cavitation as a bench unit, so it can open the same fracture. Professional units add control: a heater you can leave off, a timer set to sixty seconds instead of eight minutes, and a basket that suspends pieces rather than letting them rattle on the metal floor. Rattling is its own hazard, because a soft stone touching a hard one in a vibrating tank gets scratched. Our honest opinion after years of repairing the results: a home ultrasonic saves a few minutes and costs people stones. Use a soft toothbrush and dish soap, and bring the piece in twice a year for a check.
What should I do if a stone looks cloudy after cleaning?
Stop cleaning it and bring it in. Cloudiness after an ultrasonic or steam cycle means something changed inside the stone or in a filler. On an emerald it usually means oil or resin moved in the fractures, and GIA notes that some estimates put fracture-filled emeralds at 90 percent or more of the market. On an opal it can be crazing, the network of fine surface fractures that GIA links to heat and sudden temperature change, and GIA rates opal toughness at the bottom of its scale. On a lead-glass filled ruby it can mean the glass has been etched. GIA warns that even mild substances like lemon juice can cause changes in the high-lead content glass. None of these reverse on their own. A gemmologist needs to look before anybody cleans it again.
Sources
- GIA 4Cs: Gems and Ultrasonic Cleaners
- GIA: Ruby Care and Cleaning Guide
- GIA: Emerald Care and Cleaning Guide
- GIA: Peridot Care and Cleaning Guide
- GIA: Turquoise Care and Cleaning Guide
- GIA: Opal Care and Cleaning Guide
- GIA: Pearl Care and Cleaning Guide
- GIA: Diamond Care and Cleaning Guide
Data sourced September 2026. Hardness, toughness and cleaning guidance above comes from the Gemological Institute of America care guides linked here. Have an unknown stone checked before cleaning it by any method.
Visit Vanhess
We are a family-run studio at 2929 Barnet Highway, Unit 2424 in Coquitlam. Bring in the piece you have been afraid to clean and we will put it under the loupe, tell you what the stone is, and clean it the right way while you wait. No charge, and you do not need to have bought it from us. Call +1 (604) 653-6449 before you drive over. We also see customers from Port Moody, Burnaby, New Westminster and Vancouver.
