More on Ultrasonic Cleaners


In various articles on the web and in magazines I have often sung the praises of ultrasonic cleaning baths for cleaning firearms.  After a number of years using these appliances, the following is a summary of “do’s and don’ts”, hints, tips and pitfalls I have discovered.



Handy accessories

Things that can be cleaned using an ultrasonic cleaner (U/C)

Things that SHOULD NOT be cleaned using an ultrasonic cleaner (U/C)

Choice of solvents


Selecting a U/C

Some further reading



NEVER operate the U/C without solvent in the bowl!!!

A sure-fire way to stuff the U/C!

Bowl should be at least 2/3 full of solvent

Too much solvent?

Provided it is not spilling over, you cannot have too much solvent.

How much solvent?

Optimum seems to be enough to have the part to be cleaned with 50mm below and 25mm above the part – depending on the size of the part to be cleaned this requires a fairly deep bath.

These dimensions are not critical and the U/C will do its job with smaller dimensions, but it will take longer.

Use the supplied basket

The cleaning action works best if the parts to be cleaned are not in contact with the bowl.

There should ALWAYS be a gap between the part/s and the bottom of the bowl.

Do not stack parts on top of each other in the U/C

It will reduce the effectiveness of the U/C process

If using chemical solvent, follow OHS precautions

Chemical resist gloves, safety eyewear, breathing mask

Keep the bowl and basket clean

Wash and dry thoroughly after each use.

Bowl in a bowl

Small parts can be placed in a suitable container which in turn is placed in the U/C bowl and the bowl filled with water:

·         The container should be rigid – glass beakers (or a simple drinking glass) work best.

·         Soft plastic absorbs the U/C energy, though many people put parts in a resealable plastic bag and place this in the U/C topped up with water.  This will require a bit extra time in the U/C, but keeps the U/C bowl clean.

This is a great way of reducing the amount of ‘specialist’ solvent needed: the bul of the bowl can be filled with degassed water

Suspending parts in the solvent

Fine fishing line is handy



Dry thoroughly

Use a clean, dry, lint free cloth and/or oil free compressed air.

Protect cleaned surfaces

Once rinsed and dried the surfaces of properly cleaned parts are ‘chemically clean’ – they will oxidise/rust very quickly.


Handy accessories





ph testing kit


Wash bottle

Stainless steel forceps

ph testing kit

See note on blued steel

 Hardware stores, swimming pool supplies, garden centres


To cover range up to 60 or 70°C – homeware suppliers

Wash bottle

For rinsing

Stainless steel forceps

For getting things out of the bath


Things that can be cleaned using an ultrasonic cleaner (U/C)

Bare metal parts

Provided the solvent will not damage the metal, using that solvent in a U/C will not damage the metal:

·         Aluminium, magnesium and their alloys might stand a mild alkali solution for a short time, but in a U/C the etching action of the alkali will be accelerated.  If you are using an alkali solvent for Alu or Mag parts, keep the time in the U/C as short as possible (whether operating or not) and rinse the parts in water or neutral buffering solution ASAP once removed from the U/C

·         There are various commercial de-rusting solvents for U/C use

‘Blued’ steel

I have never had any problems with a U/C damaging the blueing of parts PROVIDED I use a mild water-based or ‘standard’ petroleum solvents, but I have heard second hand reports of damage (though I suspect the solvent/s used more than the U/C):

·         Acid (even mild) will remove bluing!  A simple and cheap ph testing kit (swimming pool supplies) can avoid a lot of heartache

Anodised Alu

Caution is advised!

Painted parts

Painted surfaces in good condition are usually OK, but…

·         Surfaces with cracked or peeling paint will be further damaged by the action of U/C


As far as I am aware, U/C has no effect on the tension of springs

Parts with adjustments

The high frequency action of a U/C can:

·         loosen lock screws/lock nuts

·         rotate screws

This particularly applies to trigger adjustments.  U/C is ideal for Walther trigger assemblies, but…

Filled engraving/stamping

Filled engraving/stamping in good condition are usually OK, but…

Surfaces with cracked or peeling fill will be further damaged by the action of U/C


Things that SHOULD NOT be cleaned using an ultrasonic cleaner (U/C)

Watches that are not waterproof

Accept that the ‘remedy’ can be a trip to a watchmaker

I have never been game enough to put ANY wristwatch in a U/C though one of my U/C has a frame to hold the watch out of the solvent while the watchband is cleaned, and this works – I do use my U/C for clock mechanisms.

Watches that are waterproof

It’s one way to find out if the watch is really waterproof

Jewellery with loose or weak mounts

Likely to become looser

Soft gemstones

They can ‘dissolve’


Choice of solvents

Degassed water with a touch of soap dissolved in it is the cheapest solvent you can use – and one of the best.

Water with dissolved soap

Degassed’ water works better than water straight from the tap!

This does not require using expensive distilled water, merely bringing the water to be used in the U/C to the boil will degas the water.

Store degassed water in a sealed plastic container (2L plastic milk bottles are excellent once thoroughly washed) and fill container to the top to reduce any more air being absorbed.

See Pre-cleaning

Cold solvent

Works OK, but hot works better – see next item

Hot solvent

60°C (140°F) seems to be the optimum

Homemade ‘special’

Per cups of degassed water:

·         Place into the ultrasonic cleaner.

·         Add ½ teaspoon of ammonia to the water in the cleaner.

·         Add 1 tablespoon of dish washing detergent into the mixture.

·         Turn the machine on and let it run for 10 minutes to mix the homemade ultrasonic cleaner solution and allow the ammonia smell to dissipate

Commercial U/C solvents

There are numerous special purpose U/C commercial solvents available and most of these will meet their design criteria

·         Only use special purpose U/C solvents for their intended use.

·         Follow the manufacturer’s instructions precisely


WILL remove blueing (and very effectively)!

Simple Green ®

Particularly for Black Powder pistol parts


Non-aqueous solvents

ß Petroleum and alcohol solvents are flammable!  Keep a fire blanket and a fire extinguisher handy

·         Do not let the solvent get too warm – the U/C solvent will warm up (considerably) when the U/C is operating - the longer the U/C is used the warmer the solvent will get and can easily exceed the flash point for the solvent.

·         ONLY use in a well-ventilated area

·         Do NOT use petroleum solvents unless your U/C has a stainless steel bowl!

Petroleum products

White Spirit (e.g. Shellite) ß

I have used these as U/C solvent successfully for years, but note the comments above re flammable solvents.

Two-stroke fuel ß

Light petroleum oil

SAE 10 (e.g. sewing machine oil) to SAE 20 (turbine oil) work well

Alcohol solvents

Methylated spirit , isopropyl alcohol or ethanol

I wouldn’t!  The flash point for these is below normal room temperature and the fire risk is unacceptable!




As a general comment, the more crud you remove from a part BEFORE using the U/C the quicker the U/C can get the remaining crud off the part/s.

Elbow grease

While a U/C is great for cleaning parts, it will not do everything – removing as much excess crud as possible before using the U/C will make it work its wonders much quicker:

·         Scrape off and/or brush away excess crud with a suitable tool that will not damage or mark the underlying surface to be cleaned.

·         Wipe off as much of any oil/wax as possible.

Boiling water

Not for plastic parts!

Great for removing excess wax.  I use an old stainless steel cooking pot: add water and parts and bring to the boil for a few minutes (not always appreciated by others in the household).

Pre-soak (for water solvent)

Windex – highly recommended as a pre-soak medium after elbow grease and/or boiling in water has been applied.  Shades of ‘My big fat Greek wedding’, but Windex is a great pre-cleaner and works wonders on the wife’s jewellery, CDs, etc.

Dish washing detergent

Pre-soak (petroleum solvents)

White spirit (e.g. Shellite)

One of my personal favourites

Break Free

I often pre-soak mechanical assemblies in Break Free for 10-15 minutes – do not soak for too long as Break Free will ‘cure’ on the part/s with time.

WD40 and the like

Another favourite, particularly if parts/assemblies are gummed up.

Penetrating oil

Another favourite, particularly if parts/assemblies are gummed up.

Carburettor cleaner ß

Will strip/etch/mark many (most?) finishes!

Brake parts cleaner

Not as bad as carburettor cleaner


Selecting a U/C


A stainless steel bowl is preferable but not essential.  Most of the smaller U/Cs (jewellery, CDs) will have a plastic bowl but this is quite serviceable for small parts and an aqueous solvent: larger U/Cs invariably have a stainless steel bowl.


Whatever size you opt for, resign yourself to the reality that you will soon have a part that is bigger.  There are U/Cs that will take a complete rifle barrel and action at 36” long and more, but they cost $$$.

Max solvent temperature

If available, go for a U/C that will handle at least 60°C

Flammability rating

If you are going to use flammable solvent/s, the U/C should have a flammability rating.


Some further reading