When ultrasonic cleaning is safe for a watch

Ultrasonic cleaning is safe for a watch only once the watch has been taken apart, and then only for the parts that tolerate it. That means a metal bracelet removed from the watch, a case stripped of its movement, crystal and gaskets, and many movement parts, cleaned in proper solutions during a service. It is never safe for an assembled watch, whatever its water-resistance rating. It is also wrong for dials, hands, luminous material, printed or painted parts, gaskets, acrylic crystals and anything glued.

How an ultrasonic cleaner works

Transducers fixed to the tank vibrate at a frequency above the range of human hearing, sending sound waves through the cleaning liquid. The waves create microscopic bubbles that form and collapse in rapid succession, a process called cavitation. Each collapse releases a small burst of energy against the nearest surface. Together they lift dirt from places a brush cannot reach: between bracelet links, under the lugs, in the teeth of a wheel. That is why the method works so well on hard, solid metal. It is also why it can harm anything soft, printed, loose or glued: the bath cannot tell dirt from paint or adhesive.

What can go in

• A metal bracelet, removed from the watch. Solid steel, titanium and gold tolerate it well. Plated bracelets call for more caution, because plating that is already worn or lifting can be loosened further. Folded or hollow links hold liquid, so they need a thorough rinse and drying.
• The case, once the movement, crystal and gaskets are out and any removable bezel is off.
• Movement parts, once the movement has been dismantled, in solutions made for watch parts, followed by rinsing and drying. The balance and pallet assemblies are usually cleaned with extra care, because they are delicate and their jewels are set in shellac.

Cleaning is one step of a full service, not a substitute for the rest. The cleaning solution takes old lubricant away with the dirt, so a movement cleaned this way must then be inspected, reassembled and lubricated afresh. A case that has been stripped needs new gaskets and a pressure test before it can be trusted near water. Longines, describing its own full service, sets out the same order. The case is taken apart, with crystal, back, bezel and seals removed and the movement separated, before it goes into ultrasonic baths. The movement is dismantled part by part and its components are cleaned in an ultrasonic machine before it is reassembled and oiled. The case goes back together with new seals where they are needed, and the finished watch is checked for water resistance.

What should never go in

• An assembled watch, mechanical or quartz, whether in a workshop machine or a household jewellery cleaner.
• Dials and hands. Cleaning can lift printing and lacquer, and aged luminous material can come loose. Old radium lume is radioactive and hazardous when disturbed. A dial that needs cleaning is a matter for careful conservation.
• Gaskets, which are normally replaced rather than cleaned when a case is serviced.
• Acrylic crystals, which are cleaned gently and, if scratched, polished instead.
• Anything glued, such as some crystals and bezel inserts. Cavitation works at an adhesive joint as readily as at dirt.
• Leather, rubber and fabric straps.
• Gem-set parts, unless a jeweller has judged the stones and settings first: vibration can loosen a setting, and some stones do not tolerate it.

Why a water-resistant watch is no exception

It is tempting to put a whole watch in a household ultrasonic cleaner because its case back says 100 m. A water-resistance rating is a test pressure under static laboratory conditions (ISO 22810 sets out the tests for water-resistant watches), not a promise about a warm, agitated bath of detergent. Gaskets age and harden, so a watch is only as water resistant as its last test. One that has not been tested for years may be far less so than its marking suggests. If the solution gets past a gasket, it reaches the dial, the hands and a movement that cannot be dried or cleaned without being taken apart. A quartz watch is no safer: its circuit and coil sit inside the same case. Even when nothing gets in, the bath does nothing for what actually wears a movement: lubricant that has thickened or migrated, which only a service can replace.

Cleaning a watch between services

Day-to-day dirt comes off without a tank. Wipe the case and crystal with a soft, dry cloth, and clear the gaps at the lugs and between the bracelet links with a soft brush. Soap and water are for a watch whose water resistance has been tested recently, and even then the bracelet is the part to wash. Casio’s care instructions for one of its watches describe scrubbing a metal band with a soft toothbrush and mild soapy water, then rinsing and drying it. The case, meanwhile, is wrapped in plastic film so that the detergent does not touch it. A vintage watch, or any watch whose seals are unknown, is better kept away from water altogether.

A solid metal bracelet can go in a household ultrasonic cleaner once it is off the watch. Removing it can scratch the lugs, so have it done if you are not used to spring bars. Rinse it in clean water afterwards and dry it thoroughly, especially between the links. If a cleaning ever leaves mist under the crystal, moisture is inside the case: have the watch opened and dried promptly, before it marks the dial or corrodes the movement.

Anything beyond that means opening the case, and that is bench work. Viattori’s repair service begins with a free assessment and a written estimate. The cleaning a watch needs is done as part of the service it is due, with gaskets replaced where needed and a watch rated for water pressure-tested at the end.

Questions

Can I put my watch in an ultrasonic cleaner?

Not with the movement inside, whatever its water-resistance rating. Ultrasonic cleaning is for parts that tolerate it once the watch has been taken apart: a metal bracelet off the watch, a case stripped of its crystal and gaskets, and movement parts during a service.

Can a metal watch bracelet go in an ultrasonic cleaner?

A solid steel, titanium or gold bracelet, taken off the watch first, generally tolerates it. Plated and gem-set bracelets need more caution, and any bracelet should be rinsed in clean water and dried thoroughly afterwards, especially between the links.

Is ultrasonic cleaning part of a watch service?

Usually, for the parts that tolerate it, once the watch has been taken apart. The movement is then reassembled and lubricated afresh, gaskets are replaced where needed, and a pressure test checks the case before the watch goes near water.

Why can’t a water-resistant watch go in an ultrasonic cleaner?

A water-resistance rating is a test pressure under static laboratory conditions, not protection against a warm, agitated cleaning bath, and gaskets harden with age. Liquid that gets past them reaches the dial and movement, which cannot be dried without taking the watch apart.

What should never go in an ultrasonic cleaner?

An assembled watch, dials, hands, luminous material, printed or painted parts, gaskets, acrylic crystals, anything glued, and leather, rubber or fabric straps. Gem-set parts need a jeweller’s judgement first.