Boing Boing Video teamed up with Theo Gray and Popsci.com to produce this video that demonstrates how you can mold steel with electrochemical machining, using a soft, cheap piece of tin — without any physical contact. Theo is the author of the book Mad Science, in which many other experiments like this are featured. Theo says:
I remember seeing a demonstration of a seemingly magic process at an engineering open house decades ago, in which a soft metal bit carved detailed shapes into far harder metals. It's called electrochemical machining (ECM), and it's so simple in principle that you can do it at home with a drill press, a battery charger and a pump for a garden fountain.
ECM is basically electroplating in reverse. In electroplating, you start with a solution of dissolved metal ions and run an electric current through the liquid between a positive electrode and the object you want to plate (the negative side). The ions deposit themselves as solid metal onto the surface of the object.
Read the whole HOWTO over at popsci.com: Carve Steel with Saltwater, Electricity and a Tin Earring
Image below: "The tin peace-sign earring acts as an electrode, etching away the metal in the hardened steel washer [left]. The imperfect results are due to the difficulty of manually maintaining an exact thousandths-of-an-inch distance between the two. Commercial electrochemically machined pieces, like this microturbine for a water pump, use sophisticated electronics to monitor the current flow and carve precise pieces [right]. (Courtesy ECM Technologies BV/ ECM Productions BV; Mike Walker)