What Not to Put in an Ultrasonic Cleaner

Ultrasonic cleaning is remarkably gentle and remarkably powerful — and that combination means a few items shouldn’t go in the bath. The same cavitation that lifts grime from a watch bracelet can loosen a glued setting or worsen a hairline crack. Knowing what to keep out protects your valuables and your equipment.

Here’s a clear, practical list of what not to put in an ultrasonic cleaner, and why.

Soft, porous or heat-sensitive gemstones

The cavitation and warmth that suit hard stones can damage softer or porous ones. Keep these out of the ultrasonic bath:

Opals, pearls and coral — porous and easily cracked, crazed or dulled.
Emeralds — commonly oil- or resin-treated; ultrasonic cleaning strips the treatment and can worsen their natural inclusions.
Turquoise, lapis lazuli, malachite, onyx and other porous/dyed stones — can absorb liquid, lose colour or crack.
Tanzanite, topaz, amber, jet and moonstone — sensitive to vibration and temperature shock.

Hard, untreated stones such as diamonds, sapphires and rubies are generally fine — but if a piece is antique, fracture-filled or you’re unsure, clean it by hand.

Jewellery with vulnerable settings or finishes

Glued or pressure-set stones — vibration can loosen adhesives and shake stones free.
Plated jewellery (gold or rhodium plate) — repeated ultrasonic cleaning can wear thin plating.
Antique, fragile or already-cracked pieces — existing weaknesses can propagate.
Costume jewellery — mixed materials and glued components don’t tolerate it well.

Certain metals and finishes

Aluminium and soft metals — strong alkaline solutions can etch or discolour them; if you must, use a material-safe neutral solution and test first.
Painted, lacquered or coated parts — ultrasonics can lift the coating.
Soft or reactive metals like raw brass can spot or tarnish in the wrong chemistry — match the right cleaning solution to the metal.

Watches and electronics (with caveats)

Non-sealed watch movements and dials — water ingress can ruin them. Only fully sealed cases by a watchmaker who knows the rating.
Items with batteries or live electronics — remove power sources first; uncoated boards may need a specialist flux-removal process rather than a general bath.

Don’t use the wrong liquid, either

Flammable solvents (petrol, acetone, pure alcohol) must never be used in an ultrasonic tank — a serious fire and fume risk. Use purpose-made water-based concentrates.
Household detergents foam, and foam kills cavitation — see our guide to ultrasonic cleaning solutions.
Bleach corrodes stainless tanks and should be avoided.

A few good habits

Use an insert basket so items never sit directly on the tank floor (direct contact can damage both the item and the transducer).
Don’t overcrowd — parts need solution around them to clean.
When in doubt, test on an inconspicuous area or clean by hand.

Still unsure?

If you’re not certain whether an item is ultrasonic-safe, it’s always better to ask first. Browse our ultrasonic cleaner range and cleaning solutions, see our guide to choosing a cleaner, or contact our Australian team for advice on your specific items.