Lithography (on limestone)

Lithography was used for printing posters right up until the 1950’s and was held in esteem above other printing techniques partly due to the prestigious effect of limestone.
In general the lithographers names remain unknown to us. They were not only quality craftsmen with detailed know-how but might also be called artists in their own right. Printing a poster using this technique could take weeks. They printed each edition on huge presses using the following process: the motif was first drawn onto the porous lithographic stone using lithographic crayons. The artist then applied the coloured ink (natural pigments derived from metallic oxides and rare earth elements, with an oil base), onto the stone’s surface.
The stone is then dampened before the sheet of paper is pressed onto it. The ink, which is oil based and thus water repellent (hydrophobic), is transferred from the non-porous part of the stone onto the paper. This makes the lithographic process different from etching (aquatinting, lino printing and woodblock printing) in which the support is cut into enabling much longer and more detailed print runs than the older physical methods of printing.
After drying, the process is successively repeated for each color until the realization of the final print. We often find positional markings on the poster margins. They are superimposed crosses which help the lithographer to position the stone to within a 10th of a millimeter of accuracy.
Thanks to precision and to the strongly pigmented color of their inks, lithographic posters reveal subtle tones of mixed color and are highly prized for their quality of finish and their artistic expressiveness. It is for this reason a great number of Swiss printers continued to use this technique until the 1960’s.

Offset printing

More rapid and efficient, offset technique replaced lithography in many countries during the period between the wars.
The development of the offset technique on the fringe of the 2nd World War went hand in hand with the generalized adoption of the four color process (CMYK) printing. This method consisted of obtaining possible colors from only four inks (cyan blue, magenta, yellow and black) applied in small points and dotted grids. This was accompanied by the development of an acetate film which could be “flashed” according to a photographic procedure comparable to heliography.
From the post war years until the present, this has been the preferred printing technique on advertising boards. The distinctive impression left by the offset printer with its agglomeration of dots is easily recognizable.

Heliography

The heliography process was a precursor of the photographic print invented by Nicéphore Niépce around 1822. Parts of a reactive surface exposed to light harden and become resistant to washing, creating a thicket layer which is transferable to paper.
Most photographic posters and photomontage made before 1940, were printed using a modern heliographic printer with a metal plate, usually copper, covered in a reactive layer. The parts exposed to light become sensitive to an acid which eats into the metal. The plate can then be retouched using a burin (intaglio).
This technique gave particular charm to posters such as those by Herbert Matter as Walter Herdeg. They are still very much appreciated.
As with lithography, the heliographic process or “Rotogravure” developed and huge rollers were used, printing with very liquid inks, which made printing in higher quality and larger quantity much easier. It is still used in today’s newspapers and magasines.

Screen printing

Each color is transferred through a silk cloth or synthetic cloth, stretched by hand over a frame which is the screen. This is a very old Chinese technique which became popular in the Occident during the 2nd World War. It was used by the May 68 students in France and became the trademark of Pop artists such as Andy Warhol and Roy Lichtenstein. It is still used to print small editions, sometimes with some surprisingly good results.
Although this method is quite mechanical, it gives surprisingly good artistic results, favoriting a tint area that enhances bright and even fluorescent coloring. At the border of this tint area, zig-zags left by the weave of the screen can be seen by using a magnifying glass. Sometimes the Four-Color process is also used in silk screen, which can be mistaken for offset in appearance.
Original Modern posters are some of the magnificent works that are achieved by using this technique.