I Guess We Have All Heard Of Electroplating,

where an electrical charge is put through a item to coat it with metal,

think chromium plating on the bright work of a car, and there is also a process known as electro etching, that is instead of placing a metal over another, the surface of one is removed to eat into the desired piece of metal, using a mask to stop all of the surface being removed, in this process a mild electrical charge is used while the desired area is exposed in the electrolyte,(liquid) using an anode, cathode, the electrolyte in this case is saltwater, above is a video of this process, and here a step by step guide to making your own etched plaque, fascinating, if I had a workshop I would have to give this a try.