Ultrasonic Cleaners: The 5 Stones You Should Never Put In

Ultrasonic cleaners are fast and effective. They use high-frequency sound waves to shake dirt loose from jewelry. That action works great on hard, intact stones. It can destroy softer or fragile gemstones. Below are the five stones you should never put in an ultrasonic cleaner. I explain the physical reasons and give practical cleaning alternatives.

How ultrasonic cleaners work — and why some stones break

Ultrasonic cleaners create microscopic cavitation bubbles in a liquid. Those bubbles collapse and release shockwaves. The shocks dislodge dirt and oils. They also force cleaning fluid into tiny cracks and along cleavage planes. If a gem has internal fractures, layers, glue, or is porous, the cavitation can widen cracks, remove stabilizers, or delaminate layers. That’s the core reason some stones must be avoided.

• Opal (including solid opal, doublets, triplets)

  Why not: Opal contains 3–21% water and has low toughness (about Mohs 5.5–6.5). Sudden mechanical stress, vibration, or rapid temperature change makes opal craze or crack. Doublets and triplets are layered: thin slice of opal glued to a backing, sometimes with a transparent cap. Ultrasonic waves push cleaning fluid into the glue layer and can force layers apart.

  Example: A 1–3 mm thin black opal doublet with a 0.2–0.5 mm glue layer can delaminate after just one ultrasonic cycle. Even solid opals can micro-fracture along internal stress points.

  Safe alternative: Clean with warm water, mild soap, and a soft brush. Dry gently with a microfiber cloth. Avoid steam and sudden temperature shifts.

• Pearl (natural and cultured)

  Why not: Pearls are organic. They’re made of calcium carbonate and conchiolin. They have low hardness (Mohs 2.5–4) and are sensitive to acids, detergents, heat, and vibration. Ultrasonic cavitation can crack the nacre layers and strip surface films. Drilled pearls can loosen when vibration agitates the glue or silk thread in a necklace.

  Example: A 7–8 mm akoya pearl strand will often stretch and the drill holes will flake after ultrasonic cleaning. Surface luster may dull from micro-abrasion.

  Safe alternative: Wipe pearls with a damp, soft cloth after wearing. Use mild soap only if needed, and lay flat to dry. Re-string pearls rather than ultrasonic clean them.

• Emerald

  Why not: Emerald is beryl (Mohs 7.5–8) but it is normally full of inclusions and fissures. Most commercial emeralds are oiled or filled with resin (natural cedar oil, synthetic resins like Opticon). Ultrasonic vibrations can force out the oil or resin, leaving the stone looking dull or causing fractures to propagate.

  Example: A 1.5 ct emerald with visible surface-reaching fissures will often lose its oil within minutes in an ultrasonic bath. The stone can look cloudy and lose apparent clarity.

  Safe alternative: Clean emeralds gently with a soft brush and lukewarm soapy water. If the stone was previously oiled, take it to a jeweler for professional treatment rather than attempting an ultrasonic cleaning at home.

• Tanzanite

  Why not: Tanzanite has a hardness around 6–6.5 and a perfect cleavage in one direction. That means it splits easily along a plane if stressed. Ultrasonic-induced shockwaves can propagate along that cleavage and cause chips, flakes, or complete breaks. Heat from cleaning can also affect color-treated stones.

  Example: A 2 ct tanzanite pendant set with thin prongs may chip at the girdle after ultrasonic exposure. Small hairline fractures often worsen under vibration.

  Safe alternative: Use mild soapy water and a soft brush. Inspect for loose settings before any cleaning. If the piece is antique or has thin facets, take it to a professional.

• Turquoise (and other porous or treated stones)

  Why not: Turquoise is porous (Mohs 5–6) and often stabilized with wax or resin to improve durability and color. Ultrasonic action can remove stabilizers and open pores, causing color loss, staining, or a chalky surface. The cleaner fluid may penetrate and remain trapped, or cause bleaching of the color.

  Example: A 10 x 8 mm turquoise cabochon stabilized with resin may look brighter after years of wear, but ultrasonic cleaning can leach out the resin within a single cleaning cycle, leaving it pale and porous.

  Safe alternative: Wipe with a damp cloth. Avoid dyes, detergents, and long immersion. If heavy soiling exists, a professional lapidary can re-stabilize the stone.

Other situations to avoid ultrasonic cleaners

• Jewelry with glued settings (cameos, inlays, doublets/triplets). Ultrasonic bubbles can dissolve glue or force layers apart.

• Antique or fragile settings. Old solder joints, thin prongs, or brittle metal work can fail under vibration.

• Plated or treated metals. Rhodium- or gold-plated surfaces can wear faster when cleaned ultrasonically, exposing the base metal.

How to decide if a stone is safe in an ultrasonic cleaner

• Know the gem. If Mohs hardness is below about 7 and the gem has known cleavage, inclusions, or stabilizers, skip the ultrasonic.

• Ask your jeweler about treatments. If the gem is oiled, impregnated, dyed, or assembled, don’t ultrasonic clean it.

• Inspect the stone and setting. Visible cracks, chips, or weak prongs mean you should not use an ultrasonic machine.

Quick list of stones generally safe for ultrasonic cleaning

• Diamond, sapphire, ruby, moissanite, and most lab-grown corundum and spinel are usually safe. They are hard, lack problematic cleavage, and tolerate vibration. Still check for loose settings or fillings first.

Final practical tips

• When in doubt, don’t ultrasonic clean. Use warm soapy water and a soft brush instead.

• Consult a professional for high-value or treated gems. They can test for treatments and advise safe cleaning methods.

• Maintain jewelry by checking prongs and re-stringing pearls regularly. Prevention is safer than aggressive cleaning.

Ultrasonic cleaners are powerful tools. Use them only for stones and settings that can tolerate shock, fluids, and vibration. For opal, pearl, emerald, tanzanite, and turquoise—skip the ultrasonics and clean gently. You’ll protect color, luster, and structure. That preserves value and beauty for years.