Rust Removal Using
Electrolysis

By Andrew Westcott

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INDEX OF SUB-HEADINGS ON THIS PAGE:
 
Introduction To The Electrolysis of Rust
An Example Of What Can Be Achieved
Safety First
Method
Special Considerations
About Cleaning Non-Ferrous Metals
A Purpose Built Power Supply
Links To Other Rust Sites

Introduction To The Electrolysis Of Rust

There have been occasions when I needed to be able to carefully remove rust from steel and iron artifacts and this page came into being as a result of my experiments in rust electrolysis. I give a respectful nod to the various rust removal pages that were in existence before this one, and to which I was able to refer whilst doing my initial experiments. I noticed that most of those sites had omitted detail which I felt was important, which is why I've tried to include everything in this one.

The idea of using electricity to convert rust back into iron is not new, and electrolysis has been used for metal restoration by collectors and archaeologists for many decades. The results can be very impressive, with shiny metal being visible after proper treatment; however, the exact requirements are sometimes poorly understood and the equipment often crude, with battery chargers often suggested.

Why use electrolysis when there are simpler methods?
Rust removal using sand blasting or other abrasives certainly cleans the metal, but this is unsuitable for very old or valuable artifacts as it is destructive, removing good metal along with the rust.

Rust can also be dissolved using strong acids, but the acid also attacks the good metal; weak acids such as vinegar just don't do the job on heavily rusted items. I required a way of removing just the rust and no more, with the hope of possibly even trying to salvage some of the rusted metal, and electrolytic rust removal seemed to be the best way to proceed.

Rust electrolysis is not some magical, or quick and easy way of removing rust. Setting up the apparatus and conditions for electrolysis needs space and is time consuming, and removing the loose converted rust once treatment has been completed also takes time and is quite messy. However, if you are prepared to put in the effort, I believe the results are worth the trouble.

Note that electrolytic cleaning doesn't work for non-ferrous metals such as copper, bronze, brass, pewter, tin or aluminium. The corrosion products found on these metals are rarely formed by electrolytic action and therefore the process cannot be reversed electrolytically. In the case of copper and tin alloys the treatment would be harmless, although I understand that aluminium could be adversely affected by the alkaline solution and so should not be subjected to this treatment.

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An Example Of What Can Be Achieved

It may be useful at this point to give an example of the kind of results that can be obtained using the electrolytic process and to describe the conditions under which they were achieved. I decided to try the process on an old horseshoe which was probably well over a hundred years old and in a particularly badly corroded condition, having spent much of its time buried in the ground where it had developed a thick layer of flaky rust.

In the photo of the shoe, you can see that it is in a very advanced state of corrosion. Note that even in the high resolution version of the image no surface detail can be distinguished, with no nails or their holes visible. Attempting to clean this would represent an extreme test of the electrolytic process, but I decided to give it a try anyway just to see what could be salvaged.

The shoe was initially prepared for treatment by using a small file to carefully remove a small area of rust on one edge in order to expose some metal, so that an electrical connection could be made using a crocodile clip. A fairly weak solution of twenty litres of washing soda was then made up at a strength of one heaped dessert spoon to every two litres - fifteen heaped spoonfuls in total, and a method of suspending the shoe devised.

Once ready, the shoe was connected as cathode and a current limited to around 200mA was applied and everything left to run for a couple of days. Once the allotted time had elapsed, the treated shoe was removed from the tub. It should be mentioned here that the solution had remained quite clear throughout and no detectable corrosion of the anode plates had occurred, this probably being due to the low current applied, and therefore the low voltage, and the enormous area of the anode plates relative to the cathode.

As the shoe was being rinsed under a tap to remove remnants of the solution, it was found that the outer layers of rust could now be pushed off using mild finger pressure, revealing a solid black and grey metallic core. Scrubbing the core using a plastic scrubbing brush wasn't completely removing the remaining black deposits, but even at this point things were looking very encouraging, with the positions of the nail holes now easily visible, and it was possible to see the grain of the iron where it had been etched by the rusting process.

A gentle scrub with a wire brush proved effective at removing the black deposits, revealing a shiny grey metal base. The nail holes themselves proved to be a bit stubborn, but I discovered that all but one could be pushed through using a small screwdriver, the remaining hole having the stump of a nail still in it. The shoe was finally given a rinse in hot water, and quickly dabbed dry using kitchen roll. The retained heat of the metal rapidly dried off any remaining damp areas, minimising the chances of too much re-rusting. Finally, to protect the shoe from further corrosion, it was given a coating of light oil.

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Safety First

The electrolyte used is mildly alkaline and although not considered dangerous, prolonged contact with the skin should be avoided. Obviously, if it gets onto your eyes, wash with copious quantities of water and seek medical attention.

The equipment involves the use of electricity, and although the voltages usually encountered in electrolysis are not considered dangerous, if the hands have been immersed in electrolyte for some time and are therefore highly conductive, even at relatively low voltages a dangerous level of current could flow across the chest area so always switch off the supply before moving connectors. There is obviously also a concern with mains equipment being sited close to liquid, so common sense must be used as regards the relative positioning of the components.

There is the issue of the production of explosive gasses: when current is passed through the electrolyte, hydrogen and oxygen are evolved at the electrodes which produce a highly explosive mixture. Ensure the procedure is conducted in a well ventilated area, and avoid sparks or flames in the vicinity. Be aware that a spark will be produced if connectors are connected or disconnected whilst power is applied and this could trigger an explosion. Always switch off the mains transformer before adjusting the electrode connectors.

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Method

A suitable container for the electrolyte should be found which is large enough to totally immerse the item to be cleaned, and I recommend one made of plastic, as this is entirely inert and non-conductive.

This photograph shows the equipment I currently use for small projects, showing the plastic
container, iron anode plates and my purpose built power supply which allows
control over the current.

Suitable material for the anodes needs to be obtained, and 0.5mm - 1mm steel plate as used for car repairs is a good choice as it can easily be cut and shaped and is inexpensive, but it shouldn't be galvanised or otherwise plated as this could effect the final outcome. Metal plate is often coated in a protective film of oil and this layer needs to be removed with a solvent or detergent before use, and obviously it must not be painted - anything which may inhibit the flow of electricity between the metal plates and the liquid has to be removed.

The bare metal anodes can be shaped to fit around the interior of the container ensuring part of each plate protrudes above the water level to enable a connection to be made. They should present a large surface area relative to that of the piece being cleaned and be able to 'see' most of the surface of the piece from all around to minimise areas of non-cleaning due to shadowing effects, as the current in the electrolyte tends to travel in direct lines rather than around corners. An anode made from a small piece of steel rod, for example, will work to a degree, but is less than satisfactory.

It should be remembered that all the anode sections, if more than one are used, must be electrically linked to each other using clips and wire and it will be beneficial to include a plate across the bottom of the tub and ideally a gauze anode across the top as well to ensure the piece is completely surrounded by anode material. An alternative would be to simply turn the piece part way through the process to make sure any surfaces which had suffered shadowing effects are treated.

An alkaline electrolyte can now be prepared, and I consider the best all-round option to be a solution of sodium carbonate, Na₂CO₃, as it is reasonably safe and also readily available at many supermarkets as washing soda. Suggested strengths for the solutions vary, but I use a 5% solution of the chemical. In order to demystify quoted solution strengths, it simply indicates the weight of chemical contained in 100mL of solution, so for example a 5% solution would involve dissolving 5 grams of chemical in water and making up the final volume to 100mL. This obviously is the same as 1 litre containing 50 grams of chemical, and so on.

You may notice a slight precipitation of white calcium carbonate produced as the sodium carbonate reacts with the calcium ions present in tap water, especially in hard water regions, this having a tendency to first make the solution appear milky, then to coat the piece and electrodes with a snowy deposit as it settles out. If wished, the solution can allowed to stand for a day or two to give this precipitated chemical time to settle to the bottom and the clear solution decanted off, or the deposits left where they settle, on the bottom of the tub out of the way as it doesn't seem to affect the outcome at all.

This diagram illustrates the components required
and the method of connection.

A low voltage DC power supply is now required, but don't just connect a battery charger to the electrodes as the low resistance of the electrolyte will allow large currents to flow causing a real risk of damage to the charger, or even fire. Even if this doesn't happen, the resulting current flow is far too high, resulting in excessive anode erosion, poor quality iron deposits at the cathode, lots of bubbling of explosive gasses and a messy electrolyte.

If a battery charger is the only current source available to you, a good work-around would be to place a low wattage automotive lamp in series with the electrolysis tank in order to reduce the current flow to a sensible value, a 12 volt 2.2 watt lamp or similar being useful for limiting the current to around 200mA or so, and for higher currents, higher wattage lamps can be used - see the 'Special Considerations' section further down the page for more information.

When connecting up, observe the correct polarity: the piece to be cleaned must be connected to the negative terminal. It is vital that the electrodes are connected the correct way round, as failure to do this right will result in the gradual destruction of the piece. A good electrical connection to the piece is also required, and will involve removing rust from a small area to reveal shiny metal to effect a good contact. Pieces consisting of more than one component, for example a gin trap, must have all the separate components electrically linked to the cathode. This is most important - don't assume the components will be electrically linked simply by their close physical contact with each other.

The photo to the left shows my equipment in use cleaning a fairly rusty pole trap. In the high resolution version of this picture you can see the way the trap is suspended in the solution and also that there are separate connections to the various parts of the trap. Also visible is the vast area of anode made up of four plates electrically connected together, and despite being in use at the time the photo was taken, the electrolyte is still clear with no bubbles being produced. This is due to the low current flowing resulting in only a small voltage appearing across the tub.

Once prepared and wired up, the piece can be suitably suspended and lowered into the electrolyte, ensuring it doesn't touch the steel plate anodes, and the power applied. Initially, there should be no bubbles coming from the cathode as the voltage differential should be insufficient to break down the water, being in the region of 1.8 volts, and if a higher voltage than this is observed, the current may be too high or there may be a poor contact to the piece. Once the reaction is complete however, a voltage rise to somewhat over 2 volts will be observed, along with the production of bubbles of hydrogen from the piece and this can serve to indicate the completion of the process, although it is a good idea to extend the time way beyond this to ensure all is complete.

After the appropriate time has passed, the power can be switched off and the piece lifted out and given an initial clean using a scrubbing brush or something similar under running water, taking care to quickly dry it afterwards - using hot water for the washing helps the peice dry due to its retained heat. The final stage is careful removal of the remaining black conversion products using a small wire brush, and to protect against further corrosion a light film of oil can be applied. There is no risk of over-treating an iron artifact using electrolysis as bare iron is unaffected by the process and therefore the piece may be left in the electrolyte indefinitely as long as current continues to flow to give it protection from corrosion.

Certain pieces may consist of components made from a combination of metals or may have iron parts with zinc or nickel plating, or galvanising. Such plating and any brass components seem quite unaffected as long as they are given cathodic protection by being also connected to the negative terminal along with the rest of the artifact, but unfortunately any corrosion present on these non-ferrous is unaffected, and would therefore require a more conventional cleaning process. I have yet to do tests with aluminium, but for now would recommend you don't place any artifacts containing aluminium components in the solution.

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Special Considerations

Electrolysis Can Damage Paint
Be aware that electrolysis can soften and lift paint; this may be due to the original surface not being properly prepared before painting, or possibly if corrosion had crept under the paint layer. Certain paints may also be softened by the electrolyte itself. So be warned that if you have an object of value with a painted surface, and if that paint is important to its value, consider an alternative to this process.

Always Have Current Flowing.
It is important to ensure that current is flowing whilst the piece is in the electrolyte, as it is the fact that it is the cathode in the circuit that protects it from corrosion. Should the piece be allowed to remain in the electrolyte without current flowing, it is possible, depending on its exact composition, that it will start to corrode, more so if the anode and cathode connections are shorted together, so if the power needs to be switched off, remove the components from the electrolyte also.

Voltage And Current.
The voltage is not critical, as long as it is higher than the minimum of around 2 volts and not so high as to be a health hazard, so something in the range of 8 - 20 volts is suitable. For good results or valuable pieces, attention needs to be paid to the current flowing. If too high a current is allowed to flow from the start, the deposited iron will be very porous and possibly become detached from the surface and the rapid hydrogen bubble production can blast off rust which could possibly have been recovered using gentler methods. If you are finding the anodes rust badly, the solution bubbles a lot and the electrolye becomes severely discoloured, the current is far too high.

Avoiding Rusting During Final Cleaning
Washing and scrubbing in water does allow the possibility of re-rusting of the piece before there is a chance to dry it completely, which can spoil the finish. One system I sometimes use helps avoid this by removing water completely from the final stages: the piece must be taken from the cleaning tank and promptly placed in a tub of clean water where it is scrubbed with a plastic brush to remove much of the now loose rust and soot-like conversion products, and well rinsed to remove the electrolyte.

From here, it is then scrubbed and rinsed in alcohol to remove the water along with more rust, and allowed to dry. Final cleaning work can now be performed on the dry piece, and when this stage is complete, the rust dust can be washed off using alcohol. Once this has evaporated, the piece can be given the final coating of oil or paint if desired.

Painting The Treated Item
I have received a fair bit of communication regarding whether the surface of the treated metal is suitable for painting without further treatment. The truth is, I don't know as I have yet to try this: my pieces are either left as they are or given a coating of oil. I welcome opinions on this matter, and will try to conduct some experiments. I would suggest though that a coating of 'red lead' primer followed by a conventional metal paint would be fine and that there would be little chance of rust forming under the paint.

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About Cleaning Non-Ferrous Metals

I have received quite a bit of correspondence concerning the cleaning of non-ferrous metals, such as copper, bronze, lead and silver. Some of these metals are often found in coins for example, so there is a requirement to attempt to clean artifacts made of these or similar metals. The corrosion found on these metals is not formed by electrolytic action and therefore the process cannot be reversed electrolytically. Up to now my experience has mainly been with the conservation of land corroded iron or steel artifacts and so I am not in a position to offer much practical advice concerning the cleaning and preservation of such pieces.

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A Purpose Built Power Supply

The idea of constructing a power supply could seem a daunting task for anyone not familiar with electronics, but for those interested, capable or who know someone experienced in such matters, I'll outline the details of such a supply in order that one could be built.

This diagram illustrates the components required to construct a regulated and
current limited power supply suitable for small to medium rust removal projects.

This circuit represents a simple power supply built around the L200 voltage regulator chip available from most electronic suppliers, and many other regulator chips will do the same job. This particular one features an internal maximum current limit of 2 amps which will be more than enough for even fairly large pieces, and lower currents can be selected when required according to the values of the appropriate resistors, values for these depending on individual requirements and guided by the table above. Slower is definitely better for rust electrolysis, and my supply has a 100mA limit on its lowest setting, with 500mA and 1 amp as intermediate settings in addition to the maximum output of 2 amps.

Regarding the circuit diagram, R4 is permanently connected and when the switch is in position 1, is set to offer the lowest required current. Position 4 bypasses any limiting resistances and invokes the internal limit which is the maximum of 2 amps, whilst positions 2 and 3 are intended to offer intermediate current settings according to the resistances used, although it is entirely possible to incorporate more than the 2 intermediate settings indicated by using an appropriate switch, it is simply a matter of personal choice. A regulated voltage output can also be set using the variable resistor if needed and this will make for a more versatile piece of equipment, although being able to vary the regulated voltage is not necessary, and a fixed resistor of a value determined by experiment could be hard wired in to produce a voltage of around 10 - 15 volts.

The regulator chip itself will need to be mounted on a decent heatsink to ensure it operates at a sensible temperature. A transformer and rectifier assembly must be built in order to supply the above circuit with direct current at an appropriate voltage, and a transformer with a secondary winding of 12 to 15 volts at a rating of 50VA should be suitable, and a bridge rectifier rated at 5 amps is suggested. Obviously, high voltage components such as the mains transformer should only be fitted and connected up by a competent person, as the voltages involved are lethal. The inclusion of an ammeter is a luxury, but can give a useful indication of the actual current flowing as this may not always be at the current limit set, and such a condition may indicate poor connections to the piece.

Regarding the actual construction, the circuit layout is not critical and it can be constructed on a single sided copper laminate board or using a tag strip, but it is important that the decoupling capacitors C3 and C4 are fitted as close to the regulator's pins as possible to avoid instability problems, and that adequate heatsinking is employed. The case for this project can be almost anything the components will physically fit into as long as there are plenty of ventilation holes to keep the internal temperatures from climbing, and any high voltage points are shielded against being inadvertently being touched by inquisitive fingers or a probing screwdriver. If a metal enclosure is chosen, I suggest the case should be earthed.

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Other Electrolytic Rust Removal References

Below are a few links to other pages currently on the web dealing with electrolytic rust removal, in random order. Hopefully between their sites and mine you'll gain a better understanding of the techniques involved.

Electrolytic Derusting

Rust Removal using Electrolysis

Electrolytic Rust Removal

Hopefully, the information I have supplied on this page
will be both informative and useful.
Happy rust busting!

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If you have any comments, or suggestions for additions or corrections to this page
please feel free to e-mail me at this address:

Copyright © Andrew Westcott 2003 - 2023
I'm happy for anyone to use this material for private, non-commercial
or educational purposes, but credit to the author must be given.
For any other use please contact me for permission.