Compositions, systems, and methods of printing an ink-jet image are provided. The or each rim retracts automatically under the action of a load which biases the or each rim from its rest position towards its working position, the load being placed on the upper surface of the tray vertically above the or each rim. To avoid the evolution of gas at the electrode surfaces the magnetic and electric fields are periodically reversed, and the electrodes are made to have very high surface areas. Some metal is allowed to pass through the shield and deposit on the coil.