You surmised correctly. Probably the most popular unit in the US
is one made by Speedbrite. They make 3 different models (sizes).
Basically each unit consists of a plastic tank that contains an
aluminum plate connected to the positive side of a DC power
supply & an liquid electrolyte. The aluminum plate is insulated
from whatever metallic item is put in the tank by a plastic
screen that covers the tank bottom. The item to be cleaned is
connected to a wire coming from the negative side of the power
supply. The item is then put into the tank & the unit turned on
(it has a built in self timer, about 10 seconds). The potential
measure across the plate & wire on the unit I have is 18 VDC. I
didn’t measure the current, it’s probably in the micro amp range.
I don’t know what the electrolyte is, all I can tell you is it
is odor free & has a soapy feel. It generates lots of suds when
shaken. The solution is supposedly safe for all non water soluble
stones. The mixing directions for the electrolyte call for 32 to
1 dilution ratio with water. One caveat that’s listed; use
demineralized water in hard water areas.
When the unit is on, a large quantity of bubbles are generated
from the item. I suspect what’s happening is a very weak form of