118 PAPER TOOLS When it comes to printing on paper, two decisions are crucial: the type of paper to use and the type of printer to choose. What paper? The choice of the most suitable printing paper depends on the final purpose of the job at hand, which impacts: finish: paper can be coated if it features a more or less shiny layer that makes colours pop, or uncoated if it keeps a natural texture; weight, which impacts durability, handling, and quality; opacity; texture. Speciality papers can be chosen to cater to unique aesthetic and functional demands of the industry; for example, paper can be: metallic, self-adhesive, waterproof, or food safe. In xerography, the drum is a negatively charged cylinder and the toner is electrically charged powdered ink. charge: carica droplet: gocciolina to engrave: incidere nozzle: ugello spur wheel: ruota dentata Printing professionally Rotary printing presses are big machines that allow newspapers, magazines, books, booklets, etc. to be printed. An image is chemically applied to a thin, flexible metallic or plastic plate and a press applies pressure to transfer ink to the material to print, which rotates around a cylinder. Offset printing is the most economical way to produce large quantities of good-quality materials. Before printing, it is possible to prepress to check that all the files are correctly processed. Rotogravure engraves the image onto a cylinder, is more expensive and time-consuming, but excellent for the quality of images. Flexography uses a flexible relief plate and is more suitable for plastics than for paper. 268 PEOPLE AND INSTRUMENTS Printing at home Printers reproduce digital images generated by computers and are basically of two kinds: inkjet, which deposit droplets of ink onto paper and plastic substrates and which can be: continuous (CIJ), creating an uninterrupted stream of ink droplets; drop-on-demand (DOD), using a print head with nozzles moving across the page; laser, which pass a laser beam back and forth over a drum, collect toner, and transfer the image to paper, producing high-quality texts and graphics. Photocopiers Photocopiers use a xerographic process which uses electrostatic charges on a light-sensitive photoreceptor to attract and transfer the toner onto paper in the form of an image. They reproduce documents and images onto paper quickly and cheaply. Photo printing machines Photo printing machines produce images on chemically sensitised paper, starting from a negative, a slide, or a digital image.