Friday, 1 October 2010

Design For Print : Gravure


Gravure is an 'intaglio' process; that is, the printing image is recessed into the plate or cylinder, 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 process, the 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 and then a blade is scraped across the surface of the plate to remove any excess ink. Paper is fed through the press on a rubber-covered cylinder that presses the paper into the recessed cells to pick up the drops of ink that from the image.
The ink is very thin and, being spirit-based , dries through evaporation in a heated drying tunnel immediately after printing. The process, therefore, unlike web-offset, does not need elaborate drying arrangements. Gravure presses do need equipment to extract the solvent fumes but the problem is now being addressed through the use of water based inks.
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, and now digital, methods of preparing the plates and cylinders has enabled the development of the modern gravure process - photogravure or rotogravure - where the printing surface is produced from film or directly from a file rather than engraved by hand.

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