PLANOGRAPHIC PRINTING TECHNIQUE

A brief mention of this type of printing, whose main technique is lithography. Lithography is based on the principle of water repellency. The matrix (Bavarian stone or zinc) is drawn with a greasy pencil and then treated with solutions of gum arabic, acid and water. In its final state, the drawn part will be able to retain the ink; the undrawn part, suitably wet, will repel the ink. Printing is carried out using a special press.

Lithograph made from a polished limestone matrix

Lithography, like woodcut printing, differs from intaglio printing not only in more subtle aspects, but also in the absence of the matrix imprint on the sheet. In flat and relief printing, the ink always leaves a very thin, imperceptible film; in intaglio printing, on the other hand, the ink has a more or less marked thickness. Finally, a mention should be made of screen printing, which is an older technique originating in China. It does not fall into any of the above classifications as it is based on a very particular process. In fact, the matrix is a silk frame in which, using special gels, the parts that must remain white are covered, and a spatula is used to pass the colour onto the sheet through the free meshes of the gel. In both lithography and screen printing, the use of photomechanical means to transfer the design onto the matrix is very widespread. However, while the use of photomechanical means is now commonplace, it is certain that we are also outside the strict field of original graphics and, to tell the truth, we are not interested in this.