At this point in the experiment, the rusty steel has been under electrolysis for about two hours. You'll find that smaller and less-corroded pieces will take less time, and large pieces will take more time.
With a fairly rusty piece of hardware and a plain steel anode, electrolysis produces a really gross layer of bubbling crud at the surface, as well as equally nasty looking precipitant at the bottom of the container.
Nasty froth from such a small part.
This chemical soup is generally a rusted brown, with little swirls of white that form patterns suggestive of the shape of the material being cleaned. Interestingly, chemists tell us that all of this is relatively benign, consisting of hydrated iron oxides, carbon dioxide, and some other trapped gasses (oxygen and hydrogen). Of course, there will also be some minor contaminants depending on what pieces are being cleaned. But, all in all, this consists of nothing more chemically than what we put in.
I’m told this can literally be disposed of down the drain, as it is rusty water with a little washing soda. That’s similar to what already goes into the municipal waste sewers, as washing machines and water softeners dump waste water through cast iron pipes, I guess.
With the power turned off and the anode removed, it is apparent why the current decreased during cleaning. The sacrificial anode steel sheet has become covered with less conductive material.
Steel sheet sacrificial anode after electrolysis.
Scrubbing the anode under tap water, reinserting it into the container, and then applying power increased the current back up to 700 milliamps.
With the power turned off, remove the formally rusted piece from the electrolysis container and visually inspect to see if any rust remains. You can take it to the sink for scrubbing, and then reinstall it in the container for further electrolysis if necessary.
The piece will be coated with a black substance that is a compound of iron different than the original rust. Some of this black coating comes off with a swipe of your fingers (which are covered in rubber gloves at this point).
Rust reduced to magnetite or fine iron metal?
I was unable to attract any of this black material using a magnet, which surprised me. Since I am not a chemist, I don’t know what it is exactly.
The black material is still affixed enough that some effort is required to remove it. I find that right approach is:
You now have reasonably bare iron-based metal which is wet and exposed to air. It is going to rust.
Dry it off with a towel (no, not the decorative ones -- those are for guests). Then, get it completely dry with a hair dryer.
Next, depending on what you have planned for it, cover it with a generous coating of WD-40, 3-in-1 oil, a rust preventative (Boeshield T-9), or paint it. To prevent future rust on tools, consider using some humidity reduction techniques.
Finally, let’s answer a few questions about what goes on in the process, and whether we can come up with a better material for the anode -- rather than the steel sheet that gets coated with corrosion.