Electrolytic Removal of Rust
by Kevin Chamberlain, Member HTPAA ( published in Tool Chest
#63, February 2002)
At our last Tool Conference, there was a Panel Discussion dealing
with the cleaning and restoration of old hand tools. This is a
key concern for anyone interested in collecting old tools, since
one rarely finds tools in mint condition in an original box. It
is much more common to find tools showing the combined effects
of correct usage, abuse, neglect and simple ageing. The primary
question is: should cleaning and/or restoration be attempted at
The answers are conflicting; some aim to restore the tool to
a brand-new appearance, eliminating all evidence of its life history.
Others think any attempt at restoration will destroy the character
and value of an antique tool.
Most think some intervention is desirable to remedy the effects
of abuse and neglect, while still retraining as much patina and
character as possible. There is an important caveat - "when
in doubt, do nothing". Cleaning and restoration of antique
tools should be done in a careful and meditative mood - otherwise
rash actions may cause loss of valuable information and/or further
Removal of rust from old tools or other artefacts may or may
not be a desirable goal. In some cases (museum specimens) stabilization
to prevent further deterioration may be all that is necessary.
Rust may be regarded as undesirable by tool users or collectors
because it obscures identifying marks, causes seizure of moving
parts, creates an unpleasant rough texture to the touch, stains
the hands and/or the workpiece, or is simply unsightly. I believe
rust removal is often justified, but the method chosen should
not alter the surface in other ways and should result in a reasonably
attractive surface appearance.
The electrolytic method of rust removal meets these aims very
well and is also a gentle, cheap and adaptable method. Electrolysis
is now being used by a wide range of artefact restorers, from
tool collectors to marine archaeologists.
In this article, I mainly aim to outline the practical aspects
of the electrolytic method so that members can try it for themselves.
Several HTPAA members have been using the method for some years
and find it very useful
What is Rust?
Rust arises from the surface oxidation of iron or steel in the
presence of atmospheric oxygen and moisture. As the rust forms,
the surface of the iron is eaten away, sometimes evenly, but often
deep local pitting occurs beneath wart-like protuberances. Rust
occupies more volume than the iron it replaces, and so moving
parts will tend to seize as they rust.
Chemically, most red rust is hydrous ferric oxide FeO(OH). If
water enters this chemical structure, yellow-brown limonite may
form FeO(OH).nH2O. Quite often, black iron oxides are
also present usually magnetite (Fe3O4),
an iron oxide which both conducts electricity and can be magnetised.
The rusting process, and the conditions which promote, inhibit
or stabilise it, are all important topics which are beyond the
limits of the present article.
Methods of Rust Removal
Rust usually binds strongly to the underlying iron or steel. Various
methods have been used to remove rust. Mechanical methods include
the use of emery paper, sandpaper or wire brushes (either manual
or powered). More aggressive methods include sand blasting or
shot blasting. Plastic bead blasting is a more recent and gentler
variant. Clearly these methods will scratch the metal surface
if the abrasives are harder than the metal. Wire brushes, for
example, do not appear to scratch hard steel surfaces but they
can be quite damaging to soft iron surfaces.
Gas flames are sometimes used to dislodge rust, relying on the
different expansion rates of the oxides and the metal in response
to heat. Simple boiling in water is also used to loosen rust.
Here the thousands of tiny bubbles which form and grow at the
metal surface may act to mechanically dislodge the rust layer.
In industry, chemical methods of de-rusting include the use of
strong acids under carefully controlled conditions. These acids
are too dangerous for home use. Vinegar or dilute phosphoric can
be used successfully at home, although the latter leaves a uniform
grey appearance which some find undesirable. Acids attack the
iron oxides directly, but also etch the mental surface to some
extent, generating hydrogen gas in the process.
Other chemical agents include the commercial product "Corro
Dip" (from Liquid Engineering International Pty Ltd) and
the traditional molasses solution. The molasses method usually
takes weeks and may work because of acids formed in the molasses
solution by fermentation. I have been told that iron or steel
objects left too long in molasses solution will eventually be
eaten away, supporting the idea of an acid etching progress. However
other chemical reactions may also be involved in this old method.
The Electrolytic Method
The electrolytic method is a cheap, gentle and effective method
which causes minimal alteration to the metal surface. It may seem
complex, but is actually easy to set up and use. It is quite safe,
provided certain sensible precautions are taken (see below). The
electrolytic method involves immersing the rusty object in an
electrically-conducting solution of washing soda (sodium carbonate).
The negative lead (black) from a battery charger is attached to
the object, and the positive (red)lead is attached to a stee1
electrode dipping into the solution. When the current is turned
on, electrochemical reduction reactions occur at the metal/oxide
interface on the object's surface. These reductions loosen the
rust layer, allowing it to be easily brushed off. These reactions
may involve the direct reduction of iron oxides to finely divided
iron. However, it is clear from observation that a major reaction
at the negative electrode involves the production of thousands
of tiny bubbles of hydrogen from the electrochemical reduction
of water. The hydrogen may in turn react chemically with the iron
oxides, or it may simply act to physically dislodge the rust layer.
Whatever the mechanism, the process does not appear to cause etching
or deposition on the metal surface. Of course, removal of rust
will reveal any damage to the surface (such as pitting) which
has already occurred.
Important Safety Precautions
1. Since pure water is a poor conductor of electricity,
a soluble salt, (called an electrolyte) has to be added to make
an electrically conducting solution. The best salt to use is sodium
carbonate (washing soda). A packet can be bought in supermarkets
for a few dollars. Washing soda solutions are alkaline and will
irritate the skin and (especially) the eyes. Always use eye
protection and gloves and wash off any spills immediately.
Do not try to use other salts - no better results will be obtained
and dangerous effects may occur. Caustic soda, for example, is
far too corrosive, and even strong solutions of ordinary table
salt will generate toxic chlorine gas at the positive electrode.
2. The battery charger is attached to the mains and must
be completely shielded from the solutions which conduct electricity.
Make sure no spills can touch the battery charger - especially
when it is unattended. The 6/12 volt leads from the charger
are relatively safe, but you may still get an unpleasant shock
if you put your hands in the solution or touch the electrodes
while the current is running. Turn off the current before making
adjustments to the electrolysis bath.
3. A major reaction occurring in the bath is the splitting
of water into hydrogen gas (at the negative electrode) and oxygen
at the positive electrode). Hydrogen will combine explosively
with oxygen or air if ignited. (Remember the Hindenburg!)
All flames (including cigarettes) must be removed from the area,
and sparks caused by touching the leads together must be avoided.
The work should be well ventilated to dilute and remove these
gases safely. Do not use this method in a confined, poorly
Preparation of the Electrolyte Solution
A sufficient concentration of washing soda is about 10 gram/litre
(about 1 teaspoon per pint). The concentration may be increased
somewhat but the results will not change greatly. Make sure all
the crystals have dissolved before using the solution.
The Electrolytic Bath
De-rusting of small pick head by electrolysis
The simplest variant of this method requires a non conducting
inert plastic container (plastic dish, box, bath, bin etc.). Some
ingenuity is needed to find containers deep or long enough for
items such as long saw blades or leg vices. After removing any
wooden handles, brass fittings, etc. from the object, sufficient
washing soda solution is added to completely submerge it.
A stainless steel strip is recommended for the positive electrode
or anode (e.g. a piece about 2-3" wide and long enough to
emerge from the solution). Ordinary scrap iron or steel can be
used, but the surface will quickly clog up with corrosion. Do
not use copper or other metals, as these will be rapidly eaten
The reactions at the anode involve the production of bubbles of
oxygen gas from oxidation of water, plus the direct oxidation
of the metal electrode. Stainless steel is most resistant to the
latter process, but even it may show some minor pitting after
a while. The anode should be brushed clean at intervals. The red
lead from the battery charger should be clipped to the anode where
it emerges from the solution. If this attachment clip dips under
the surface, it will be eaten away. The negative lead (black)
is attached to the rusty object. In this case, the attachment
clip may be submerged under the solution - corrosion does not
occur at the negative electrode (cathode). It is very important
to have good contact at the attachment point, so these should
be cleaned by wire brush or emery paper. The object and the positive
electrode should be separated by at least a few inches. If they
are allowed to touch, a short circuit will occur and the battery
charger may be damaged.
The Battery Charger
Any 6 or 12-volt battery charger will work, provided it can produce
a few amps of direct (DC) current. A current of about two amps
at 12 volts is typical (a charger with a current meter is useful
as it shows you what is happening). If several objects are attached
in parallel, or a very large object is attached, the current may
rise. Be careful not to exceed the capacity of your charger. The
current may be reduced by increasing the separation between the
object and the anode or by diluting the solution with water. A
car battery would also work as a DC power source.
Hydrogen bubbles forming on the object's
surface during electrolysis
Once the circuit is completed, tiny bubbles will stream from both
electrodes. The time required for effective de-rusting will vary
from 30 minutes for small objects (such as auger bits) to many
hours for large objects such as a leg vice. Overnight operation
is common. No harm is done by leaving the circuit on for long
periods, as long as the charger does not overheat or gases do
not build up in an unventilated area. After a time the object
should be rotated to avoid "shadow" effects (uneven
de-rusting). If part of the objet has been left projecting above
the solution, the object should also be inverted to de-rust the
exposed part. As time passes, some of the rust will fall off and
sink to the bottom of the container. When enough time has elapsed
(learned mainly by experience), turn off the charger, remove the
object from the bath and rinse off the electrolyte with water.
The residual rust will now appear as a dark surface sludge which
can be easily removed with a hand wire brush or plastic scourer.
This is less messy when done under water (e.g. in a water-filled
bucket). After rinsing and thorough drying, the object will now
appear free of red rust, but there may still be a thin layer of
closely-adherent black oxide.
For certain antique artifacts, this grey-black appearance may
be quite attractive. However, brief power brushing will quickly
remove this thin layer and give a progressively shiny and burnished
appearance (appropriate for items such as plane blades).
Rust sludge remains on object surface after electrolysis
Clean steel surface after sludge has been brushed
Baking in an oven for an hour or two at about 150°C (300°F)
is an option which will give the objects an attractive bronze-yellow
patina, deter further rusting and protect against hydrogen embrittlement
(see below). Alternatively a rust inhibitor such as RP-7 may be
applied, or the object simply oiled or waxed to deter future rusting.
If only part of the objet was submerged there will usually be
a faint "tidal mark" where the object emerged from the
solution. This is one reason to seek containers large enough to
submerge the whole object at once. I find that intact japanning
is not usually damaged by electrolysis, but loose paint of any
type will be stripped off and this is often a useful feature of
The method works best on objects that are electrically well-connected.
Ideal objects for de-rusting by this method include augurs, axe
heads, saws, single bow hand shears, plane bodies, cast iron pots
etc. Whenever the object has multiple parts, the electrical contact
between the parts will affect the results obtained. If the contact
points are coated with rust, dirt or grease, little current will
flow from one part to the next and de-rusting may be slow. If
only a few parts are involved, it is easy to connect each part
separately by providing several branches from the negative lead
or use short leads to connect each part to the next using clean
Other Variants of the Electrolytic Method
1. The bath itself may be made of stainless steel and used as
the anode (positive electrode while the rusty object is suspended
in the middle of the solution without touching the container.
This method maximizes the size of the anode and allows current
to flow to the object from all directions - thus minimizing shadowing
2. The opposite of the above. Hollow vessels such as iron pots
are filled with the electrolyte solution and attached to the negative
lead, while the anode is suspended in the middle of the solution.
This allows excellent de-rusting of the inside of such pots. A
similar method has been used to remove rusty encrustations from
the inside of cannons found in sunken ships.
De-rusting the inside of an iron pot
using a suspended anode
3. Small items may be placed on a stainless steel grid suspended
in the solution and electrically connected to the negative (black)
lead. The rusty items make electrical contact with the grid and
do not need to be individually connected to the lead. However
the de -rusting will proceed rather slowly unless the items have
been cleaned where they touch the grid. Small chains and other
intricate objects with connected parts may be de-rusted using
Localised de-rusting of the sole of
an infill plane using an electrolyte-soaked sponge
4. To avoid immersion of objects such as wood-infill planes the
bath may be replaced by a solution-soaked sponge or cloth which
lies between the object and a stainless steel plate which acts
as the positive electrode. The negative lead is attached to the
object and current flows only through the soaked sponge. Be careful
to avoid any short circuits. More solution should he added to
the sponge periodically as it heats up and tends to dry out. This
method can be used to de-rust small parts of artefact quite precisely
without wetting the whole object.
Hydrogen Embrittlement of Steel - A Cautionary Note
Atoms of hydrogen absorbed by steel are known to enter the lattice
of iron atoms and prevent the layers from sliding past each other
easily. This causes the steel to become more brittle and liable
to crack. The absorption of hydrogen by steel is a familiar problem
in industry which arises during steel refining, heat treatment,
acid pickling or electro-plating. It can also happen as a result
of simple corrosion. The standard remedy is to bake the objects
in ovens to drive out the absorbed hydrogen (200°C for four
hours would be a typical regime in industry). The simple passage
of time is also known to cause loss of hydrogen from steel. Hydrogen
embrittlement may occur to some extent during electrolytic de-rusting.
This may be a cause for concern with saws or other edge tools.
It might be wise to wait a while before setting saw teeth after
prolonged, electrolytic de-rusting. Alternatively, baking the
tool in the oven for hour or so at about 150°C (300° F)
should remove absorbed hydrogen. Note that this baking temperatures
is low enough to leave the temper of most steels unaffected. Since
hydrogen embrittlement is reversible, it should not cause too
much anxiety. I believe that the advantages offered by electrolytic
de-rusting justify wider experimentation by tool collectors. As
more experience is gained clearer knowledge of its advantages
and disadvantages will emerge.
Problems with Stainless Steel Anodes
Some thoughtful correspondents have pointed out that the use
of stainless steel for the positive electrode (anode) may have
some undesirable consequences. Most stainless steels contain high
percentages of chromium and nickel which may be released into
the bath as the anode is slowly eaten away. These are likely to
be released initially as soluble cations just as the iron is released
initially as ferrous ions. However, since all three cations are
being released into an alkaline solution, they are likely to be
immediately converted to insoluble hydroxides or oxides and form
encrustations on the electrode or fall to the bottom as sediments.
In this bound form the nickel and chromium are likely to be less
hazardous but nevertheless waterproof gloves should always be
worn when working with the bath and the bath sludge should be
disposed of appropriately. It may be better to avoid the problem
entirely by using simple iron electrodes and brushing the sludge
Jane and Mark Rees. Tools. A Guide for Collectors. Published by
Roy Arnold, Suffolk. 1996. p22.
Nathan Lindsay. Cleaning Rusty Tools. Electrolysis Made Easy.
Ted Kinsey. The Electrolytic Rust Removal FAQ www.bhi.co.uk/hints/rust.htm
FAQ Derusting with Molasis, www.steamengine.com.au/ic/faq/mollasis.html
Metal Conservation (Marine archaeology) http://nautarch.tamu.edu/class/anth605/
Acknowledgements: Thanks to Kees Klep and Peter Williams for
sharing their experiences of this method and to Tony Blanks, HTPAA
member from Tasmania and skilled netsurfer, for providing valuable
website information. Warren Hewertson and Doug McIver provided
constructive review of the text.