Rust Removal by Electrolysis - A Detailed Illustrated Tutorial, page 18
3. Preparing a Relic for Electrolysis: How To Make A Good Electrical Contact
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Quite often, the following happens: an electronic circuit is assembled - everything seems to be connected correctly, and the electrolysis machine is turned on, but the process does not start. The reason for this malfunction is the artifact's rusty surface: the rust is not electrically conductive and, therefore, blocks electric current.
To allow dc current to run through the iron object being de-rusted, it is necessary to make a good metal-to-metal electrical contact between the object and the cathodic power connector - an alligator clip or a battery clamp. Choose a few electrical contact points on the iron object: a couple of connection points - on the part to which a cathodic power clamp will be attached, and one contact point - on the artifact's part that will be submerged into electrolyte, which will provide contact with the electrolytic solution.
The next step is to file, scrape or grind a connection point to remove the rust off. I used a small file to remove the rust at two connection points on the edge of my iron axe to expose some metal.
Filing Rust Off at One Connection Point
Filing Rust Off at Another Connection Point
And then I filed the rust off at the connection point on the axe's part being submerged.
Finally I wind steel wire around the part of the axe blade, to which a cathode will be attached, making sure the wire touches the de-rusted connection points. I could just connect the cathode to one of those connection points, but using the steel wire as the cathode wrapped around the relic will increase the contact area, thus, increasing the amount of electric current flowing through the object, and, therefore, speeding up the electrolytic cleaning.
Using Steel Wire as a Positive Electrode
If there are original holes in the iron object being derusted, they can be the best spots to be used for connection points. One can make solid metal-to-metal connections at these spots by grinding the rust out of them first, and then embedding new bolts and nuts into the holes for attachment of the cathode.