The ultrasonic cleaner – is it essential for clock repair?

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Ultrasonic cleaner by L&R
Ultrasonic cleaner by L&R, model 140

Is the ultrasonic cleaner indispensable for clock repair? The short answer is “no”. I know many in clock repair who hand clean clock movement parts, have had good success over the years and are not about to change their ways.

In my view, there are so many advantages to having an ultrasonic cleaner you will wonder why you did not have one in the first place. Indeed, these are many reasons why the ultrasonic cleaning system is widely used across many different industries.

Follow me as I explain why the ultrasonic cleaner can help you with the cleaning of most clock movements.

What is an ultrasonic cleaner?

An ultrasonic cleaner is a machine that comes in various sizes and used to clean many things. Ultrasonic cleaning uses cavitation bubbles induced by high-frequency pressure (sound) waves to agitate a liquid. The agitation produces high forces on contaminants adhering to substrates like metals, plastics, glass, rubber, and ceramics. This action also penetrates blind holes, cracks, and recesses.

The result is very fast and effective cleaning.

20 minutes is usually sufficient

What to clean and what cleaner to use

Most brass and steel clock parts can be cleaned. Leave out leather hammers and any specific items you do not want to be exposed to a liquid. Although plain water does work, whenever possible, it is best to use a water-based detergent in the ultrasonic cleaning process. Water-based solvents are nontoxic, nonflammable, and environmentally friendly. In the absence of commercial water-based detergents, a few drops of Dawn will do.

What not to put in an Ultrasonic cleaner

Never use any kind of flammable liquid in an ultrasonic cleaner; it is plainly dangerous. Liquids with relatively low vapour pressure (ie. lower boiling points) may nebulize or convert to a small spray when exposed to cavitation in an ultrasonic bath. This means tiny mist-like droplets will be dispersed into the air, somewhat akin to an ultrasonic humidifier. These droplets combine with air to create a perfect storm for combustion. This includes flammable liquids in sealed plastic or open bags or containers, glass etc..

As a general rule, there is no safe way to use flammable liquids in any stage of clock repair. Avoid flammable liquids altogether in an ultrasonic or even when cleaning by hand.

L & R is a reputable brand; this one has a drain and a heater

Ultrasonic cleaning works

I use an ultrasonic cleaner when I clean most clock movements because of the precision and thoroughness of the process. There is nothing I know of that cleans lantern pinions better than an ultrasonic cleaner.

In the main tank, I use hot water with Deox 007 mixed with water. Deox 007 is a biodegradable, non-toxic, mildly acidic, de-oxidizer and de-greaser which has a slightly slippery feel, meaning the surface tension is low and will transmit sound easily. Using hot water also speeds up the degassing process. If your ultrasonic cleaner has a heater, use it. Note that water/liquid which is too hot will strip lacquered parts.

If the movement is particularly dirty, a pre-cleaning with degreasing soap (dish detergent) and water is recommended.

Generally, a 15-20 minute time period is all that is required to thoroughly clean a dis-assembled movement. Machines have various output powers so timing may have to be a bit of an experiment for your particular machine.

Dial removed showing time and strike movement
Dial removed showing time and strike movement in as-found condition

Clock parts must be rinsed in a bath after a period of time in the ultrasonic, so the “dirt” in the solution is not a big concern. I wash dishes by hand and by the end of the task the water in the sink is sometimes pretty nasty, that’s why rinsing dishes is important. The bath can be simply warm water or a special rinsing solution. I use two bathes of warm water.

After cleaning in an ultrasonic cleaner; the difference is noteworthy

The drying phase is critically important. All parts must be dried immediately after the cleaning and rinsing process. Rust forms very quickly on steel parts. I use either a hairdryer or time my wife’s baking and leave the parts in the residual heat of the oven, usually for about half an hour or so.

Methods may differ but I take the liquid out of the ultrasonic cleaner after each use and store it in a plastic jug. I have a fairly small US so when the liquid gets too dirty I filter it through some coffee filters. And by dirty, I mean a very dark brown. When I perceive that it isn’t cleaning effectively I just dump the liquid and refill. Since the cleaning liquid is biodegradable I pitch it on the back lawn.

Exceptions to the rule

Aluminum parts with ammonia-based cleaners will turn brass dark. Personally, I feel ammonia can be harmful to both brass and humans and I would be very careful. The ammonia combined with the overcleaning of the ultrasonic and the wrong solvent will start by differentially dissolving the zinc from the surface of the brass leaving a washed-out pitted surface. However, having said that, if you research ammonia on clock forum sites it’s still not clear who is right on the issue.

I would also not put floating balance escapements or hairsprings in an ultrasonic cleaner.

Old hammered brass movements are much more fragile and sensitive to both chemicals (ammonia especially) and the impact of ultrasonic cleaning. Since old brass, which is very porous, does not take kindly to being placed in an ultrasonic cleaner this 175-year-old English bell strike, for example, was cleaned entirely by hand.

Scottish tall case clock with English bell strike movement

Final thoughts

Can you get by without an ultrasonic cleaner? Absolutely! However, unlike other tools in your clock repair arsenal, the ultrasonic cleaner is one that not only will save valuable time but may produce spectacular results.

Although an ultrasonic cleaner is a labour-saving device, it is not a panacea. It will make things clean, but it won’t make everything look like new. If the metal is very tarnished, nothing that I know of will remove that oxidation, aside from fine abrasives.

If your budget allows, It is worth spending money on an ultrasonic cleaner.

2 thoughts on “The ultrasonic cleaner – is it essential for clock repair?

  1. Hi Ron,
    I see many posts concerning the ammonia issue. I use Zenith 251 NA. I actually wrote to the chemist at Zenith chemicals. He said the non ammoniated chemicals will not affect brass with stress corrosion cracking (SCC). Even the ‘amines’ are fully changed and will not affect the movement. So, I am with you on water based cleaners, and I like my ultra sonic cleaner too. I love to see the transformation from dirty to incredible.


    1. Thanks. SCC, I must remember that. Safety in the shop is so important regarding the uses of cleaners. I use Deox 007 in my US and have had excellent results.


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