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The Printing of Postage Stamps
Since 1840, when the first two stamps of the world made their debut, practically all known systems of printing have been used in their production. There are three main groups of printing techniques: surface printing, or letterpress, lithography and intaglio printing.
Surface printing is the oldest method. It was perfected in 1440 by Johann Gutenberg, who used movable letters. For surface printing, the ink is normally transferred to the paper by raised type. There is no ink in the hollows and these areas appear as white on the paper. In the printing of postage stamps, especially initially, the letterpress method was used. In this technique, many faults and mistakes occurred in the process of production and of printing, and the printing plate or cylinder was also frequently damaged. This resulted in numerous errors and stamp varieties.
Surface printing can be detected on postage stamps by several typical marks. The design usually has sharp contour lines; it is even and straight, the layer of ink is minimal and sometimes there can be discerned on the back of the stamp a slight embossing of the design into the paper (especially in overprints).
In lithography, there are no relief parts or hollows on the printing plate or cylinder. This printing method is based on the fact that areas of the plate which are greasy accept ink but reject water, whereas the rest of the surface absorbs water and rejects ink. In the early days of stamp production, printing stones were mostly used for the production of stamps. At present, flat printing is mainly represented by offset printing. Stamps printed in this manner do not have the sharp contour outlines found in surface printing. Although the design is flat and the layer of ink very thin, the design is not embossed into the paper.
Intaglio printing is the exact opposite of surface printing. In intaglio printing, the hollows contain the ink and print whereas the relief parts are clean and leave areas without print. The ink is firstly dabbed onto the plate or cylinder, then the ink is removed from the surface and it remains only in the hollows and lines. The ink is then printed onto the paper. The most common methods of intaglio printing used in the production of stamps is line engraving and photogravure. In intaglio printing, the appearance of the stamps is quite different from the previous two methods. There is a thicker layer of ink giving the stamp an almost ‘plastic’ appearance.
A special type of printing is called embossing. With the help of a pair of matched dies, a relief design – with or without colour – is impressed into the stamp paper. Usually embossing is combined with another printing technique which adds the remainder of the design, including the frame, in colour. Nowadays, many stamps are printed in a number of colours. For every colour, a separate plate or cylinder is used. Printing presses can combine different techniques, for instance – steel engraving and photogravure.
In modern printing shops, rotary presses have superseded the plate printing machines, just as printing machines supplanted the primitive hand presses.
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