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The Lithographic Process
Lithography was invented by a man named Alois Senefelder in the 1790's. Since then, it has been used as an artist medium but it has also been the basis which developed into the industrial, high speed production printing that is done today. Its relationship to industrial processes is important for artists to note for conceptual and technical reasons. Lithographic prints are characterized by the their flatness, and the wide variety of tones and marks that can be achieved, especially by a good printer.
I am going to discuss lithography in terms of the older techniques and its use as an artists medium.
- The first thing that needs mentioning is the main chemical principle of lithography, which is that water and oil do not mix. In our case, oil is the base of the ink and drawing mediums we use. The printing matrix from which we use could be an aluminum plate or, my favorite, a perfectly flat piece of limestone.
- An image is chemically bonded to the stone using an "etch". The basic etch is nitric acid suspended in vehicle of gum arabic. The strength of the etch depends on how greasy the drawing materials are. The greasier the image the stronger the etch will need to be. The etch is buffed into the stone using soft cheesecloth and allowed to dry and harden.(see etching the stone for a more detailed description)
- A thin film of water is applied to the stone or plate using a sponge.
- The image is inked with a roller. For black ink, a wooden roller covered in leather is often used. The water film repels the oil based ink from the non image areas, and a layer of ink is built up within the image area.
- The paper is placed on the inked image. A tympan sheet, which is usually an acrylic or lexan sheet, is placed on top of that. The scraper bar is lowered onto the tympan. The press is designed to put a great deal of pressure on the stone or plate with the scraper bar. The press then moves the stone or plate by either a hand crank or motor. The scraper bar scrapes across the tympan exerting even pressure across the inked image. The ink is thus transferred onto the paper.(see also fig.6 for a diagram on how the basic lithographic press works.)
Etching the stone: preparation, drawing, and etching.
Printing the lithograph.
photoplates:halftones, and digital processes.