Text 4 Gravure

V. Compose a plan and write a short summary of the text.

Before the modern version of gravure was invented, the basic principles had long been applied: pictures were engraved on plates and printed on flat-bed presses. The introduction of photographic methods of preparing the plates has enabled the development of the modern gravure process - photogravure or rotogravure — where the printing surface is produced from film, rather than engraved by hand.

The process Gravure is an 'intaglio process'; that is, the printing image is recessed into the plate, rather than being flat, as in lithography, or raised, as in letterpress. The image consists of cells engraved into a copper-plated plate or cylinder. On the gravure press these cells are filled with liquid ink. The cells vary in depth, so that they will leave the required amount of ink on the various parts of the printed image. A blade called a 'doctor blade' is pulled across the surface of the plate or cylinder to remove any excess ink. The paper is fed through the press on a rubber-covered cylinder which presses the paper into the recesses to pick up the drops of ink that form the image.

The ink is very thin and, being spirit-based, dries through evaporation immediately after printing, The process, therefore, unlike web-offset, does not need elaborate drying arrangements (although these presses do need equipment to extract the solvent fumes).

Characteristics of gravure Because of the cell structure, type can look fuzzy close-to, as the cell walls break up the fine detail. However, gravure printing of photographs is often superior to that produced by other processes, as gravure gives a 'true' halftone effect: the darker areas of the photograph actually carry more ink as they are printed from the deeper cells. Also, photographs printed by gravure have greater contrast between light and dark areas, as a heavy film of ink is carried. They have good detail (unlike the type) as finer screens are used than with other processes. These qualities are evident even on cheaper papers.

The gravure press Most gravure printing is done with web-fed machines which, as in other web-fed processes, use reels of paper and folds the printed paper. The machines are usually very large, printing up to 128 pages of A4-size and running at speeds of 50,000 impressions per hour

Uses of gravure Sheet-fed gravure is used for fine-art prints and high-quality art and photographic books, as well as the higher-denomination postage stamps, weekly magazines, mail-order catalogues and colour supplements. It is also used for some kinds of packaging, printing on cellophane, decorative laminates and wallpaper.

Exercises :

Дата добавления: 2014-12-23