* HOW DOES PRINTING MACHINE WORK*.

              * HOW DOES PRINTING MACHINE WORK*

What is printing?

Printing means reproducing words or images on paper, card, plastic, fabric, or another material. It can involve anything from making a single reproduction of a priceless painting to running off millions of copies of the latest Harry Potter. Why is it called printing? The word "printing" ultimately comes a Latin word, premĕre, which means to press; just about every type of printing involves pressing one thing against another.

Although there are many different variations, typically printing involves converting your original words or artwork into a printable form, called a printing plate, which is covered in ink and then pressed against pieces of paper, card, fabric, or whatever so they become faithful reproductions of the original. Some popular forms of printing, such as photocopying and inkjet and laser printing, work by transferring ink to paper using heat or static electricity and we won't discuss them here; the rest of this article is devoted to traditional printing with presses and ink.

Printing is hard, physical work so it's usually done with the help of a machine called a printing press. The simplest (and oldest) kind of press is a large table fitted with an overhead screw and lever mechanism that forces the printing plate firmly against the paper. Hand-operated presses like this are still occasionally used to produce small volumes of printed materials. At the other end of the scale, modern presses used to print books, newspapers, and magazines use cylinder mechanisms rotating at high-speed to produce thousands of copies an hour.

Types of printing

The three most common methods of printing are called relief (or letterpress), gravure (or intaglio), and offset. All three involve transferring ink from a printing plate to whatever is being printed, but each one works in a slightly different way. First, we'll compare the three methods with a quick overview and then we'll look at each one in much more detail.

• Relief is the most familiar kind of printing. If you've ever made a potato print or used an old-fashioned typewriter, you've used relief printing. The basic idea is that you make a reversed, sticking-up (relief) version of whatever you want to print on the surface of the printing plate and simply cover it with ink. Because the printing surface is above the rest of the plate, only this part (and not the background) picks up any ink. Push the inked plate against the paper (or whatever you're printing) and a right-way-round printed copy instantly appears.

• Gravure is the exact opposite of relief printing. Instead of making a raised printing area on the plate, you dig or scrape an image into it (a bit like digging a grave, hence the name gravure). When you want to print from the plate, you coat it with ink so the ink fills up the places you've dug out. Then you wipe the plate clean so the ink is removed from the surface but left in the depressions you've carved out. Finally, you press the plate hard against the paper (or other material you're printing) so the paper is pushed into the inky depressions, picking up a pattern only from those places.

• Offset printing also transfers ink from a printing plate onto paper (or another material), but instead of the plate pressing directly against the paper, there is an extra step involved. The inked plate presses onto a soft roller, transferring the printed image onto it, and then the roller presses against the printing surface—so instead of the press directly printing the surface, the printed image is first offset to the roller and only then transferred across. Offset printing stops the printing plate from wearing out through repeated impressions on the paper, and produces consistently higher quality prints.

Photo: The three most common types of printing: Left: Relief—Raised parts of the printing block (gray) transfer the ink (red) to the paper (white rectangle with black outline at the top) when the two are pressed together. Middle: Gravure—Grooves dug into the printing block transfer the ink to the paper when the paper is pressed tightly into them. Right: Offset—A rotating cylinder (blue) transfers ink from the printing plate to the paper without the two ever coming into contact.

* HOW DOES PRINTING MACHINE WORK*

The metal plates are curved around a printing cylinder and press against a series of rollers, which dampen them with water and then brush them with ink. Only the lacquered parts of the plate (those that will print) pick up ink. ... The blanket cylinder then presses against the paper and makes the final print.