If you’ve been thinking about adding an ultrasonic machine to clean your watch parts, you may have heard that ultrasonics will damage your parts and that you should never use an ultrasonic except to clean your cases and bracelets.

Ultrasonic machines can be extremely efficient and completely safe as long as you know what to do and what not to do.

Today I’m going to go over what’s important to look for in a machine.

I’m going to test three professional grade cleaners against a couple DIY cleaners and if you stick around, I’m also going to show you the secret to getting the best results without breaking the bank.

So even if you’ve been using an ultrasonic machine for a while now, there’s always something new to learn and what you don’t know could be holding you back from being a better watchmaker.

Important: When available, we use affiliate links and may earn a commission!

Do Professional Watchmakers use Ultrasonics Cleaners for Watch Parts?

The first burning question to answer is, do professional watchmakers use ultrasonics to clean their watch parts?

The answer is yes, of course they do.

High End Elma Watch Part Cleaner
High End Elma Watch Part Cleaner

Because of the volume of movements professionals might be servicing, the highest end cleaning machines that they use combine both rotating baskets along with ultrasonics. This Provides the fastest cleaning of watch parts possible. But these high-end part cleaners can go for well over 10 grand.

Is it possible to get the same results in a bench top ultrasonic watch cleaner when speed is not the issue?

You bet it is and I’m going to show you how to do it.

Can Ultrasonic Cleaners Damage Watch Parts?

In order to understand the limitations of ultrasonics, you need some context to understand the main differences as well as the similarities between one of the professional grade machines and the type of machine you’re probably going to be looking at.

If you watched my last video on using IPA, you saw me put a vintage pallet fork into an ultrasonic with L&R cleaner.  After just a five-minute cycle, the pallets stones came out.

Pallet Fork Damaged in Ultrasonic Machine
Pallet Fork Damaged in Ultrasonic Machine

  If you’re cleaning newer parts, this is not as likely to happen, but when you’re cleaning vintage parts, the chances of damage go up. This is because of the quality of the parts or the condition of the shellac.

For me, it’s just not worth the risk of putting them in any type of watch cleaning machine, ultrasonic or not. It’s not about the metal becoming damaged.

 It’s about the condition of the shellac and whether or not the cleaning action of the ultrasonic is going to separate the shellac from the metal, which could loosen a jewel.

That is really the main concern.

Professional Grade Ultrasonic Watch Cleaning Machines

A professional watchmaker is going to put all the parts into their cleaning machine, including the pallet fork and the balance wheel.

The difference between you and them is that they’re typically working on higher end movements that have higher quality parts, so they’re less likely to see shellac damage. even if they do, they have the equipment and the experience to either reset the stone or to just replace the pallet fork.

As a home watchmaker, if you damage a pallet fork or a balance, you have just created a problem that you may not be able to solve.

Benchtop Ultrasonic Machines

Benchtop ultrasonics are designed primarily for using detergents, not solvent-based cleaners. Professional grade machines can use solvent-based cleaners and rinses safely because these machines have built-in ventilation as well as being explosion-proof.

Professional Grade Machines are Explosion Proof
Professional Grade Machines are Explosion Proof

When you use solvent-based cleaners in a home ultrasonic machine, not only do you have to deal with the smell of fumes, but there’s always a risk of these fumes igniting from either some sort of spark or even a malfunction inside the machine.

And then of course, disposing of the old solvents also becomes an issue.

Getting the Most out of an Ultrasonic Watch Cleaning Machine

Now to get the most out of your cleaning routine, you first must know how these machines work.

These machines work from an ultrasonic sound wave that usually comes from the bottom of the tank, and these sound waves bounce off the top surface of the liquid and return to the bottom of the tank, creating what’s known as a standing wave.

Standing Waves
Standing Waves

These standing waves produce tiny bubbles that implode onto the watch parts, kind of acting like little jets that knock off the dirt in the grease.

This is what’s known as cavitation.

Depending on the frequency or the kilohertz that your machine is producing, there are gaps between these standing waves, which are known as dead spots.

This picture is of a piece of glass that’s been etched by overexposure in an ultrasonic machine.

Ultrasonic Dead Spots
Ultrasonic Dead Spots

The light areas show where the standing waves are, and the darker areas are these dead spots that I talked about.

It is in these dead spots where the least amount of cleaning takes place. The lower the kilohertz that your machine runs at, the larger and more powerful the cavitation bubbles are, but they are also more condensed together, creating larger dead spots.

As the kilohertz increases, the cavitation bubbles become smaller and have less scrubbing power, but the bubbles start to spread out more so that the dead spots are smaller.

Remember this because we’re going to come back to it in just a minute.

What to Look for in an Ultrasonic Watch Cleaner

Now when you’re looking for an ultrasonic machine, the first thing you want to make sure of is that it has the ability to run at least 40 kilohertz.

Fortunately, this is by far the most common wavelength that you will find in an ultrasonic, and if you look at the high-end ELMA machine, this is the same frequency that they run at for the cleaning cycle.

Just know that anything operating well below 40 kilohertz produces larger, more aggressive cavitation bubbles and probably should not be used for watch parts.

High End Ultrasonics run at Multiple Frequencies

Now another big difference between a premium machine and your basic ultrasonic is that they’re going to be able to run at multiple frequencies.

As an example, ELMA’s P30H ultrasonic machine can run at both 40 kilohertz for cleaning and 80 kilohertz for rinsing, which is ideal. But the price of these machines quickly jumps up to the $1,300 range, which pretty much knocks them out of contention for most home watchmakers.

Two Categories of Cleaning Fluids for Ultrasonic Watch Machines

There are two basic types of cleaning fluids used for ultrasonic machines, solvent-based and water-based.

Many of you might be concerned about using water-based detergents on watch parts because you’ve heard of the potential for rusting.

If you go on any watch form and mention that you’re cleaning and rinsing watch parts with water, just wait for the reaction because everybody has an opinion. The fact of the matter is that the use of water in part cleaning and rinsing is nothing new and is an accepted practice throughout the watchmaking industry.

Let me just quote you a couple sources.

The Theory of Horology

The first is from page 283 of the theory of horology under how to clean.  If you’re not familiar with the Theory of Horology, it is the textbook used by every watchmaking school in the world that trains watchmakers for almost every watch brand out there.

“Soap diluted with water will act chemically on certain foreign bodies and dissolve them”.

Then it goes on to say,

“water cannot be eliminated with benzene, for example, but alcohol will do the job”.

Watchmaking by George Daniels

My next source is probably the greatest watchmaker in modern history, George Daniels. In his book Watchmaking on page 403, he says, and I quote,

“when the watch is completed and ready for final assembly after gilding, it will be adequate simply to clean the components in an ultrasonic soapy water bath. Any stains should first be removed by refinishing the component part after the soapy water has been absorbed, rinse in fresh warm water, and then in methylated spirits to absorb any traces of water”

How to Safely Use Water to Clean Watch Parts

So, you have the leading Swiss training organization on watchmaking, as well as George Daniel, whose handmade watches now sell for millions of dollars, both referencing the use of water and then displacing it with alcohol.

Now with that said, if you’re going to use water, you have to be smart about it.

Use Distilled Water

At a minimum, I would use distilled water because a lot of well or tap water will have heavy minerals in it. Distilled water will have very little minerals in it. Remember that you’re going to be following the distilled water with an IPA rinse anyway, so it should rinse away any trace minerals that may be left behind.

  If you can find it at a reasonable price, deionized water is 100% mineral free, but it’s expensive.

Drying Watch Parts Cleaned in Water with Heat

Now the final thing is, you want to be able to dry the parts with heat. I use a food dehydrator which works perfectly.

Food Dehydrator for Drying Watch Parts
Food Dehydrator for Drying Watch Parts

 It has a lid, I can set the temperature anywhere from 95 to 150 degrees, and it blows a light flow of warm air over the parts.

Always Start by Pre-Cleaning

Before you put the watch parts into a cleaner, to get the best results in your ultrasonic, it all starts with pre-cleaning.

If you just strip a movement down and throw it in the machine, you’re probably not going to get the best results.

During disassembly, I always pre-clean inside the barrel to remove the heaviest grease. I’m also running a Q-tip with a little IPA over the jewels so that I can see them when I’m doing my inspection.  It also helps to loosen up any dried lubricant before I peg out the jewel holes.

Cleaning the Balance Wheel and Pallet Fork

Now after I inspect the balance and the pallet fork, I put them into a diamond cleaning jar of either hexane or Trichloroethylene to soak, because as I’ve said many times, I always clean them separately from the other parts.

Cleaning Balance Wheel & Pallet Fork in Hexane
Cleaning Balance Wheel & Pallet Fork in Hexane

I can soak these for as long as I need because these solvents, I’m using don’t affect the shellac.

If I need to do any repairs or any parts need to be polished, I also pre-clean them before I put them in my cleaning liquids.

Smaller watch parts get loaded into brass part holders, and larger parts can be suspended by wiring peg wood to separate them in the ultrasonic cleaner from the other parts in the jar.

Small Parts Are Held in Baskets
Small Parts Are Held in Baskets
Large Parts Are Suspended
Large Parts Are Suspended

Ultrasonic Watch Cleaner Testing Parameters

There are as many cleaning solutions available for the ultrasonic machine as there are opinions on what’s the best to use.

If you have one that works well for you, drop it in the comments. I’d love to hear what you use.

To test the cleaners today, I’m going to apply six different types of watch lubricants on these rotors.

Lubricants used In Ultrasonic Cleaning Test
Lubricants used In Ultrasonic Cleaning Test

Lubricants Used for Testing

The first is Kluber P125, probably the stickiest barrel grease there is and MolyKote DX, which is known as one of the hardest greases to clean and  another barrel grease, 8213.

On the lower part of the rotor, I’m going to apply a drop of HP 1300 on the left, 9010 in the middle, and 9504 on the right side of the rotor.

Lubricants Applied to Rotor going in ultrasonic watch cleaner
Lubricants Applied to Rotor

Timed Cleaning Cycles

For testing purposes, I’m going to do a 10-minute wash cycle, followed by a five minute rinse cycle, and then a two-minute rinse in IPA alcohol on all the cleaners we test. This is followed by 10 minutes of dry time in the food dehydrator, set at 120 degrees.

Costing Out the Different Cleaners

For the purpose of costing these products out, I’m going to figure the price based on using 10 ounces of fluid in a mason jar, and for the IPA rinse, I’m using 99% alcohol calculated at $1.40 per jar.

Testing Solvent Based Ultrasonic Cleaning Solutions

L&R Extra Fine

Now the first cleaner I’m testing is L&R Extra Fine.

You should always follow your machine’s warnings about not using anything that’s flammable in it, and I’m not recommending that you do what I’m about to show you. This is purely for my own curiosity.

 Since the first cleaners I am testing are going to be solvent based and flammable, I’m going to do the testing without using the heater to see how well they clean in just room temperature water.

One issue with L&R is that if it mixes with water, it will emulsify. This creates a nasty goo that if it gets on the parts, it’s going to be pretty hard to clean off.

Because of that, the first rinse will be in L&R’s rinse number 3, and then the second rinse will be in the IPA.

Costing Out L&R Extra Fine

Now when costing this out, it came to $4 per jar for the L&R cleaner and the rinse, for a total of $9.40 including the IPA.

If you clean 5 watches before changing out the fluids, that will work out to about $1.90 per clean movement.

Degassing the Fluids

Since all the fluids are going to be new, I will be doing what’s known as degassing. Degassing is a function that some machines have which removes the gas bubbles that are in the liquids which interfere with the ultrasonic machine’s cleaning ability.


If your Ultrasonic watch cleaner doesn’t have this function, you can just let it run for about 20 minutes with no parts in it, or if the liquids have been sitting out for at least 24 hours, the gas bubbles should be gone.

Now looking at this rotor, here is the Kluber P125, the MolyKote DX, the 8213, the HP1300,

the 9010, and the 9504. I’m going to suspend the rotor from a wire and run it through the wash in two rinse cycles.

As you can see, even the hardest to clean grease is completely gone. There are no signs of it whatsoever.

L&R Cleaning Results in ultrasonic watch cleaner
L&R Cleaning Results

I would point out that the amount of grease that you initially saw should be pre-cleaned off anyway, but there is really no denying that the L&R is very effective, which is probably why it’s one of the most popular.

Testing Zenith 251NA

The next cleaner marketed to watchmakers is Zenith 251NA Concentrate. This is a non-ammonia-based concentrate that’s mixed one part cleaner to seven parts water.

Even though it’s labeled as flammable on the bottle, once it’s mixed with water, who knows how flammable it really is? It’s certainly a very low odor cleaner, so it has that going for it.

One advantage of it is that it can be rinsed with water.

The biggest disadvantage is that after you use this cleaner once, it can gel up after about 24 hours, and it becomes unusable. According to Zenith, after using the product just one time, the residual oil and grease from the clean movement can cause bacteria to grow in the cleaning solution, which is what’s causing it to gel.

Costing out Zenith 251NA

But at about $1 to one clean movement, including the IPA, I mean, it’s worth looking at, especially if you can clean more than one movement in a day.

So, here’s the rotor with the same lubricants applied to it. In this time, I’ll do a 10-minute clean cycle with a five-minute rinse cycle, and then the IPA rinse.

Zenith Test Results in ultrasonic watch cleaner
Zenith Test Results

So, when looking at the rotor outside of the dryer, you can see that it removed all the oils and the grease just as well as the L&R.

So, at about half the cost, it will definitely do the job.

Testing Naphtha

The last solvent-based product we are going to test today is good old Naphtha, sometimes called lighter fluid.

It’s readily available in most places, depending on where you are in the world. People like Naphtha because you can buy it in smaller quantities if you’re only cleaning an occasional watch.

Costing Out Naphtha

Naphtha comes in at around $20 a gallon, which works out to about $3 worth of product, including the IPA.

Cost-wise, if you’ve got five clean movements before changing out the fluids, that works out to about 60 cents per clean.

Naphtha Test Results in ultrasonic watch cleaner
Naphtha Test Results

Performance-wise, you can see that it performed just as well as the L&R and Zenith, but at a fraction of the cost.

The one real difference is that the pro-grade cleaners have metal brighteners in them. So if you have any grungy or stained movements, Naphtha alone is not going to brighten the parts.

Cleaning Watch Parts with Water Based Detergents

Now, the key to getting great results with water-based cleaners is knowing how your ultrasonic machine is really designed to work and finding the sweet spot based on these four things.

  1. the frequency
  2. the fluid temperature
  3. cleaning time,
  4. the detergent you’re using.

Since most machines you will be looking at have a fixed frequency of 40 kilohertz, there’s not much you can do to change that. You also want to get clean parts as fast as possible without having them in the machine for extended periods of time.

One of the biggest advantages of water-based cleaners is that now you can introduce heat to the cleaning procedure.

Heat Improves the Ultrasonics Cleaning Ability

Heat affects the ultrasonic waves that are produced by your machine in a couple of different ways. As the fluid temperature increases, it improves the distribution of the cavitation bubbles.

This reduces the dead spots, but at the same time, it will reduce the scrubbing force of those bubbles, almost as if your machine was running at a higher kilohertz.

Just be aware that there is a limit to how much heat you want to use in your tank. At 40 kilohertz, the cavitation bubbles that are produced will have their highest scrubbing action when the fluids are at about 95 degrees.

As the heat increases, the bubbles scrubbing ability slowly starts to decrease up until you get to about 176 degrees, where these cavitation bubbles have no cleaning ability at all.

That’s one reason why most manufacturers set the maximum temperature of their machines at 180 degrees.

The key here is finding the right temperature for the cleaning solution that you’re going to be using.

Foil Testing the Advantage of Heat

Now, to demonstrate the difference that the water temperature has on cavitation, I’m going to be doing what’s called the foil test.

First, I’m going to do it at room temperature, and then I’m going to repeat the same test at 137 degrees.

Foil tests are used to show the effectiveness of the cavitation bubbles in any ultrasonic machine.

I’m going to drop a test panel into my machine.  I’m going to run it for a five-minute cycle at room temperature. Then I will repeat the same test by bringing the water temperature up to 137 degrees and running a new test for five minutes.

First let’s look at the holes produced in the foil when it ran at room temperature.

 Foil Test at Room Temperature in ultrasonic watch cleaner
Ultrasonic Foil Test at Room Temperature

Notice the size of the holes and how closely they are grouped together. What this test is showing us is the scrubbing intensity of the cavitation bubbles as well as the concentration of the bubbles in one area.

  Foil Test at 137 degrees in ultrasonic watch cleaner
Ultrasonic Foil Test at 137 degrees

When you look at the foil test that was run at the higher temperature, the first thing you’ll notice is that there’s only a couple pin holes in the foil. This indicates that the cavitation bubbles are just not as strong.

What’s interesting is that the larger areas on the foil where you can see that it’s been indented.

Foil Test Showing Spread Out Cavitation Pattern in ultrasonic watch cleaner
Foil Test Showing Spread Out Cavitation Pattern

This indicates that the bubbles are spreading out, and they’re covering a larger area inside the tank. This is like machines running at a higher kilohertz.

Ultrasonic Cleaning Detergent

The fourth factor is the actual detergent itself. Some cleaners will come with a recommended temperature on the label. If it does, that’s where you should probably start at.

If it doesn’t, the general guideline for ultrasonics and detergents to work the best is to heat the fluid to 65% of the fluid’s boiling point.

Now since water boils at 212 degrees, that means our fluid temperature in theory should be set at about 137 degrees.  I used that temperature in the foil test.

Heating the Ultrasonic Tank AND Fluids

Now for the next two tests, I’m going to set the tank around 137 degrees, insert the jars, run the degas function, and I’m going to bring all the fluids up to temperature.

My machine takes about an hour to get there on its own, so I can speed up the process a little by just adding hot tap water to the tank.

I’m going to run the same cycles of a 10-minute wash with a 5-minute water rinse, but because the IPA is flammable, I’m not heating the IPA, I’ll just add the cold jar into the tank for the final 2 minute rinse.

Then I’ll put everything into the dryer at 120 degrees for about 10 minutes.

Testing Elma Red 1.9

The first water-based cleaner I’m testing is Elma Red 1.9. Elma Red is a concentrate diluted 1 part to 9 parts of distilled water. It’s very low to no odor when mixed and can be disposed of right down the drain as it’s classified as non-hazardous.

I will apply the same lubricants to a rotor and run the same cleaning process, 10-minute wash, 5 minute, and a 2 minute rinse.

Now the downside to Elma Red, at least in the US, is that I haven’t found any suppliers that carry it.

Regardless, I still order it from Cousins UK when I need to get other parts or supplies from them, so it’s no big deal.

Costing Out Elma Red

Now for me, the shipping cost is almost as much as the cleaner, but even still, this liter bottle makes 30 10 ounce jars, and when you add the cost of the IPA, it only comes out to around $2.60 for 5 cleans, so it’s just over 50 cents per movement.

Elma Red Test Results
Elma Red Test Results

Out of the dryer now, you can see that it’s cleaned off all the lubricants to the same level as the solvent-based cleaners we used.

Testing Dish Soap on Watch Parts

Now if you’re in one of those places where you just can’t get anything, or you really just want to go as low cost as possible and still have good results, you can always use Dawn dish soap and water.

Dawn and water are an amazing parts cleaner combo with many advantages for the home watchmaker. Now for you guys outside the US, Fairy would probably be a very similar product to Dawn.

Costing Out Dawn Dish Soap

For this test, I’m going to mix up 1 ounce of Dawn to 9 ounces of water. So at about 15 cents per ounce, with the cost of the IPA added, if you got 5 cleaning cycles, that works out to about 31 cents per clean movement.

So I set the tank to 137 degrees, degas the fluids, and bring everything up to temperature. I’ll run the clean cycle again for 10 minutes with a 5-minute rinse, and then a 2 minute rinse in cold IPA, followed by another 10 minutes in the dryer.

Dawn and Water Ultrasonic Results
Dawn and Water Ultrasonic Results

And as you can see, the lubricants have been completely removed by this combination of Dawn and water.

Now considering the overall cost, the availability, and the ease of disposal, this ratio of Dawn to water, along with running the tank at 137 degrees, is a great option for cleaning your watch parts.

Just remember to do 2 rinse cycles in water, just to make sure that you remove all traces of the detergent before you do the IPA rinse.


Make Sure to Use 99% IPA for Final Rinse if you use water.

By displacing the water in these last 2 test runs, and drying the parts with heated air, you can be assured that you don’t have to worry about your parts getting rusty, and you can get great results in your ultrasonic machine.

So, if you have a favorite cleaner that you want to try out, you can do the same test that I showed you in this video.

Investing a small amount of time doing experiments to find your favorite cleaner’s sweet spot with the tank temperature and the cleaning time is absolutely worth your time investment.

If you follow these guidelines in your cleaning routine, you will improve your cleaning game, and you will consistently get cleaner watch parts time after time, and that will help you to become a better watchmaker.