Cleaning Theory and Ultrasonic Risk

Cleaning a movement removes several distinct kinds of material that accumulate over years of running: old lubricant that has oxidised and thickened into a gum that increases friction rather than reducing it, fine metallic dust produced by ordinary wear at pivots and tooth contacts, and airborne dust and fibres that enter through the case even when it is kept reasonably closed. Left in place, this residue does not merely make a movement look dirty; the thickened oil actively increases friction and can eventually stop the watch, while abrasive metallic dust suspended in old oil accelerates wear at exactly the points it collects.

Ultrasonic cleaning works by immersing parts in a cleaning solution while a transducer generates very high-frequency sound waves through the liquid, creating and collapsing millions of microscopic cavitation bubbles that scrub contaminants out of crevices, pivot holes and tooth spaces far more thoroughly than a brush or hand-wipe could reach. This is genuinely effective and is standard professional practice — but it is effective precisely because it is a fairly aggressive mechanical process, calibrated by solution choice, temperature, duration and frequency to the specific parts being cleaned.

Misused, the same cavitation action that removes gummed oil can also damage a movement: a hairspring's fine, evenly spaced coils can be distorted or tangled by cavitation turbulence if cleaned incorrectly or for too long, shellac-based friction joints (still found in some pallet-fork and roller-table constructions) can be dissolved by the wrong solution, and assembled parts with different materials or delicate finishes can suffer galvanic or abrasive damage if cleaned together in a solution or cycle not suited to all of them. This is one of the main reasons professional cleaning is done with parts disassembled and separated by type, in solutions and cycle lengths matched to the class of part, rather than as a single generic wash of an intact movement.

Running an assembled watch, or even a case back removed but movement otherwise intact, through a jewellery-cleaning ultrasonic tank — a well-intentioned but risky practice occasionally attempted at home — is a common cause of exactly this kind of damage, because a home ultrasonic tank has none of the solution selection, disassembly and part-sorting discipline that makes professional ultrasonic cleaning safe, and can dislodge or damage a hairspring, wash away lubricant that then is not replaced, or force contaminated solution into places that then cannot be properly dried or re-oiled.

The safe general rule, consistent with the rest of this academy's guidance, is that cleaning a movement is a disassembly-dependent, solution-dependent, part-sorted process carried out by a trained watchmaker, and that an intact case or movement should never be placed directly into a home ultrasonic cleaner in the hope of a quick improvement, however clean the outcome might look immediately afterward.