Ultrasonic Cleaners Explained: What They Are, How They Work, and What Fluid to Use
Ultrasonic cleaners have moved from industrial workshops and dental surgeries into homes across the UK. You can now buy a decent one for under £30, and they're remarkably effective at cleaning things that are awkward to clean by hand jewellery, glasses, watch straps, dentures, small mechanical parts, and more.
But there's a lot of confusion about what fluid to use, what you can and can't clean, and whether they're actually worth buying. This guide answers all of it.
How Does an Ultrasonic Cleaner Work?
An ultrasonic cleaner is a small tank filled with liquid. A transducer on the base or side vibrates at ultrasonic frequencies, typically between 20,000 and 40,000 Hz — creating millions of tiny bubbles in the liquid. These bubbles form and collapse rapidly in a process called cavitation.
When a cavitation bubble collapses near a surface, it produces a tiny but powerful jet of liquid that dislodges dirt, grease, tarnish, and other contaminants. This happens across the entire submerged surface simultaneously, including in crevices, engravings, and places a brush or cloth could never reach.
The result is a thorough, even clean that's gentle enough for delicate items but effective enough to strip carbon deposits off engine parts.
What Fluid Should You Use?
This is the question that causes the most confusion. The short answer: it depends on what you're cleaning.
Water alone works for light cleaning dust, fingerprints, and loose dirt on items like glasses and watch straps. But water's surface tension limits the effectiveness of cavitation.
Water with a drop of washing-up liquid improves performance significantly. The surfactant reduces surface tension, allowing the cavitation bubbles to form and collapse more effectively. This is fine for general cleaning of non-sensitive items.
Dedicated ultrasonic cleaning fluid is the best option for most tasks. These fluids are formulated with the right surfactants, pH level, and anti-tarnish agents for specific applications. A quality ultrasonic cleaning fluid will clean more effectively than water alone and protect the items being cleaned.
Specialised solutions exist for specific industries medical-grade fluids for dental instruments, degreasers for carburettors and mechanical parts, and precious-metal-safe solutions for gold and silver jewellery.
Never use: flammable liquids (petrol, acetone, alcohol), bleach, or strongly acidic or alkaline solutions. Flammable liquids are a serious explosion risk in an ultrasonic cleaner. Bleach and strong acids can damage both the items and the tank.
What Can You Clean in an Ultrasonic Cleaner?
Jewellery: Gold, silver, platinum, and most gemstones clean beautifully. Diamonds, sapphires, and rubies are safe. Avoid pearls, opals, emeralds, and any porous or organic stones ultrasonic vibration can damage them.
Glasses and sunglasses: Excellent for removing the built-up grime in hinges and nose pads that cloth cleaning misses. Safe for all lens types including coated lenses.
Dentures and retainers: Very effective at removing plaque and staining. Use cold (not hot) water and a denture-safe solution.
Watch straps: Metal bracelets come up like new. Remove the watch head first if it's not water-resistant.
Coins: Effective for removing surface dirt without the abrasion of manual cleaning. Collectors should be cautious, though any cleaning can reduce numismatic value.
Small mechanical parts: Carburettors, gun parts, 3D printer nozzles, and other precision components. Use an appropriate degreasing solution.
Razor heads and electric shaver foils: Quick and effective. Use plain water.
Musical instrument mouthpieces: Brass and silver mouthpieces clean well. Check with the manufacturer for lacquered instruments.
What Should You Not Put in an Ultrasonic Cleaner?
Some items can be damaged by ultrasonic vibration or by immersion in liquid:
- Pearls, opals, turquoise, and porous gemstones
- Watches that aren't water-resistant (the head, not the strap)
- Wood, leather, or fabric items
- Soft plastics that could warp
- Electronics (unless in a sealed housing)
- Items with loose settings or damaged prongs the vibration can dislodge stones
When in doubt, check whether the item is safe for immersion in warm water. If it is, it's probably fine for ultrasonic cleaning. If it isn't, keep it out of the tank.
Tips for Getting the Best Results
Use warm water. Around 40–50°C is ideal. Warm water improves cavitation efficiency and helps dissolve grease. Don't use boiling water it can damage both the cleaner and some items. (use cold water for plastics such as those found in dentures and retainers.)
Don't overload the tank. Items need to be fully submerged and shouldn't be touching each other or the base of the tank. Most cleaners come with a small basket or tray use it.
Change the fluid regularly. Once the fluid looks dirty, it's less effective. How often depends on what you're cleaning, but for regular home use, every few sessions is a good starting point.
Time it right. Most items need three to five minutes. Very dirty items might need ten. Running longer than necessary wastes energy and doesn't improve results much, if it's not clean after ten minutes, the issue is usually the fluid, not the time.
Are Ultrasonic Cleaners Worth It?
For anyone who regularly cleans jewellery, glasses, or small parts, an ultrasonic cleaner pays for itself quickly both in time saved and in the quality of the clean. A £25–40 home unit will handle everything most people need.
Professional-grade units with larger tanks and higher frequencies are available for specialist applications, but for household use, a basic 600ml–800ml tank with a 40kHz frequency is more than adequate.
The main thing that makes a difference day-to-day isn't the machine it's the fluid. Using the right solution for the job is what turns a decent clean into a professional-quality result.
Choosing an Ultrasonic Cleaner
For home use, look for a tank capacity of at least 600ml (enough for a couple of rings and a pair of glasses), a timer function, and ideally a heating element. Budget models without heaters still work, you just need to fill with pre-warmed water.
For cleaning carburettors, gun parts, or other larger mechanical items, you'll need a bigger tank, 2–6 litres is typical for hobbyist use.
Frequency matters less than marketing suggests. Most home and professional units operate at 40kHz, which is a good all-round frequency. Higher frequencies (80–120kHz) produce a gentler clean and are used for delicate items like circuit boards, but they're rarely necessary for home use.
