Rust Removal via Electrolysis – An Overview

On the way home from work last night I was reading the woodworking sub-reddit and I noticed several posts about rust removal.  It seems like very few people are aware of how cheap and easy it is to use electrolysis to remove rust from tools.

Over the past few years I have used a pretty simple setup to strip the rust / paint off of my tools and I have been VERY happy with the results.  That said, I am in no way shape or form an expert on the subject so I do not know if this is appropriate for any collectable tools, but it works great for my users and involves little if any harsh chemicals or fumes.  I have never used EvapoRust but I used Navel Jelly and other similar products when I worked on the restoration team at the USS Missouri Museum and this process is safer and cheaper.  Plus there are no air-born particulates.

Electrolysis uses direct current (DC) power to transfer material from one piece of metal to another via a solution.  In our case, we are transferring Iron atoms from a sacrificial piece of metal to the tool in order to convert some of the “Red Rust” (ferric oxide) to “Black Rust” (magnetite).   The piece of metal to be cleaned is connected to the positive (red) terminal and the sacrificial piece is connected to the negative (black) terminal.  As the electricity travels through the solution, iron atoms are transferred from the sacrificial steel to the tool (along with some oxygen from the water) changing the Fe2O3 into Fe3O4.   In the process, the red rust that is not converted into black rust will come off and drop into solution.  Black rust is non-destructive (it does not flake) and it does not hold moisture like red rust so it actually helps to protect the metal from further rusting.  I’m not a chemist so take this all with a grain of salt.

The supplies you need:

-plastic container (I use a bucket or boot tray depending on what I am cleaning)

-12 volt DC power supply (I use an old laptop power supply)

-Baking Soda or Washing Soda

-Scrap Iron or steel (no stainless or galvanized)

-Wire

-Alligator clips (optional)

-Scrotchbrite sanding pads for cleanup (I use the “between finish coats” grit)

Power Supply

Most of the setups I have read about online used car batteries or battery chargers but I use a laptop power supply that I was able to get one from my IT department for free since it was being sent to recycling.  While they are lower power than the typical battery charger they are smaller, sealed (i.e. water resistant), and in my case free.  The lower power simply means the parts need to stay in solution for a longer time and I have a feeling there is less chance of damaging the parts being cleaned.

The modifications are simple, cut off the plug that goes into the laptop and identify which of the wires is positive and which is negative (the internal wires may already be color codes otherwise use a multi-meter).  I then connected longer color coded wires (in my case I used heavy gauge speaker wire from radio shack) and attached an alligator clips to make it easier to connect the parts being cleaned.

The Cleaner

May of the posts I read recommended using “washing soda” mixed with the water however I find baking soda is much easier to come by and since “washing soda” is simply a stronger version of baking soda you  can simply use more of the baking soda.  Typically I use around a tablespoon of baking soda per gallon of water, but I am not precise in my measurements.

Sacrificial Metal

For the process to work, the negative terminal needs to be connected to a piece of sacrificial steel or iron.  I have read that if stainless steel (or other steels containing chromium) is used the process can release toxic gases and will contaminate the water with heavy metals.  Additionally, you should avoid galvanized steel as you may end up Zinc plating your tool.  I typically use re-bar because it is cheap and easy to find but I think cast iron works faster (maybe the porous structure increases surface area?).  What is most important is the piece of metal should have a lot of surface area as this will dramatically speed up the cleaning process.

This piece(s) of metal will eventually become unusable due to the buildup of corrosion however in my experience you can use them for multiple cleanings.

The Process

Note: we are dealing with electricity and water together so be careful.  Connect everything with the power supply unplugged and if possible, use a GFI outlet.

Getting things started is simple: connect the part to be cleaned to the red wire; the sacrificial metal to the black wire and submerge both in the solution of water and baking soda, making sure the two pieces are not touching.  Now set you bucket outside and plug it in (this process can release small amounts hydrogen gas which is flammable in enclosed spaces so do this in a well ventilated area), you should see a bubbles forming on the surface for the part being cleaned or streams of bubbles reaching the surface within a few seconds.  Now sit back and wait.

How long?  That is the 64 thousand dollar question.  It is going to depend on the strength of your power supply, the level of corrosion, the strength of your cleaning solution, the surface area of your parts, etc.  I will typically check on the progress every few hours but seriously rusty parts I often leave overnight.

IMG_4960
Note the use of a nickle plated bolt, DON’T DO THIS.

 

When the parts are done, they will be black in color and you should see none of the telltale texture of rust.  Once it comes out of the solution you can either leave the black magnetite in place or remove it with a fine grit sanding pad.  You then want to dry the part quickly and apply oil as flash rust can appear quickly.

 

Sources:

http://myweb.tiscali.co.uk/andyspatch/rust.htm

http://www.woodcentral.com/cgi-bin/readarticle.pl?dir=handtools&file=articles_363.shtml