are applied to the paper by lines heat transfer – such as early fax machines or modern receipt printers that apply heat to special paper, which turns black to form the printed image inkjet – including bubble-jet, where ink is sprayed onto the paper to create the desired image electrophotography – where toner is attracted to a charged image and then developed laser – a type of xerography where the charged image is written pixel by pixel using a laser solid ink printer – where solid sticks of ink are melted to make liquid ink or toner Vendors typically stress the total cost to operate the equipment, involving complex calculations that include all cost factors involved in the operation as well as the capital equipment costs, amortization, etc. For the most part, toner systems are more economical than inkjet in the long run, even though inkjets are less expensive in the initial purchase price. Professional digital printing (using toner) primarily uses an electrical charge to transfer toner or liquid ink to the substrate onto which it is printed. Digital print quality has steadily improved from early color and black and white copiers to sophisticated colour digital presses such as the Xerox iGen3, the Kodak Nexpress, the HP Indigo Digital Press series, and the InfoPrint 5000. The iGen3 and Nexpress use toner particles and the Indigo uses liquid ink. The InfoPrint 5000 is a full-color, continuous forms inkjet drop-on-demand printing system. All handle variable data, and rival offset in quality. Digital offset presses are also called direct imaging presses, although these presses can receive computer files and automatically turn them into print-ready plates, they cannot insert variable data. Small press and fanzines generally use digital printing. Prior to the introduction of cheap photocopying, the use of machines such as the spirit duplicator, hectograph, and mimeograph was common. 3D printing 3D printing is a form of manufacturing technology where physical objects are created from three-dimensional digital models using 3D printers. The objects are created by laying down or building up many thin layers of material in succession. The technique is also known as additive manufacturing, rapid prototyping, or fabricating. Gang run printing Gang run printing is a method in which multiple printing projects are placed on a common paper sheet in an effort to reduce printing costs and paper waste. Gang runs are generally used with sheet-fed printing presses and CMYK process