Glossary

Offset printing is a flat printing process: Printing and non-printing elements of the printing plate lie in one plane. The printing areas of the printing plate are inked whilst the non-printing areas are not inked. In the printing process the printing plate is moistened and inked. The ink is transferred by a rubber blanket to the material to be printed on. This transfer process from the plate cylinder via the rubber cylinder on to the printing cylinder with the material to be printed is necessary so that no fountain solution (moistening film) is transferred to the material to be printed. Offset printing is therefore an indirect printing process since printing is not directly from the printing plate on to the material to be printed on.

The letters stand for the colours Cyan, Magenta, Yellow and Key or black (both interpretations of the letter K being common). CMYK are the primary colours of subtractive colour mixing. CMYK are the scale colours of multicolour printing. Black serves to increase contrast.

Offset printing is done from metal printing plates. These plates are given a light-sensitive coating. The printing areas are transferred by exposure, these days mostly by Computer to Plate technology (CTP). The printing areas are hardened by exposure. In the subsequent development and fixing these areas are retained and they later take up the ink. The non-printing, non-hardened areas are washed off and do not take up any ink, only water.

The euroscale or European scale is a standardised colour chart used in Europe that specifies the printing colours yellow, magenta, cyan and black (CMYK) , the sequence of the printing ink application in photo printing, the saturation and the hue used in four-colour printing. The scale is available as a reference work or as a colour chart and shows the shades possible in printing.

The material on to which the printing is done is of course of central importance to printing quality. The choice of papers is wide and the descriptions of the types depend on the paper manufacturers and the paper wholesalers. It is therefore recommended that designers purchase ranges of paper from one or more wholesaler. In any event it is necessary either to specify a unique paper type description with the printing enquiry or to ask the printer to submit a paper sample with their printing quotation.

With coated papers, immediately after paper production a coat that consists mainly of chalk is applied. This coat by and large prevents the printing ink from penetrating the paper fibre, which allows fine matrix points to appear much sharper and to be reproduced more accurately. Coated papers can therefore be printed to a significantly better standard and to a higher quality than uncoated ones. Because of their special characteristics these types are also known as art and image-printing papers. There are coated papers with glossy and matt surfaces. The best for printing are glossy coated papers. On the other hand, matt coated papers do not reflect, which is of particular benefit when looking at or reading the content.

The three basic colours of additive colour mixing (red, green, blue) that cannot be processed in printing techniques are the colours of light that combine to make white.