The technique of lithography, "engraving on stone"
Lithography
"Lithos" in Greek means "stone." Lithography is an printing technique that reached its peak in the nineteenth century and uses a special stone known as "lithographic stone," found in Germany. The process is highly original. In wood carving, one of the earliest techniques practiced, one simply carves away all areas that should not be inked. Then, once the work is complete, the surface is inked using a roller or a cloth pad soaked in ink, and the image is transferred onto fabric, parchment, or paper. However, it's clear that this method remains very limited. Only flat areas can be produced, and the finesse of lines, or "strokes," is severely restricted. With lithography, we proceed by creating a matrix through "chemical abrasion," a process that will be described later. I have practiced this extensively, and as soon as possible, I will include some images of lithographs I made several decades ago. The lithographic press is visible in the drawing below. Incidentally, I am the author of this drawing, which is thus a pen-and-ink exercise with hatching. The rendering on your screen, or by your printer, will not allow you to appreciate its full subtlety. Not important.
What can be distinguished in this illustration?
From behind, the lithographer is preparing his inks—or rather, his ink, since each printing pass is monochrome. In the foreground, in front of this man: a lithographic stone, placed on the press. Two others are standing vertically along the machine, nicknamed the "horned beast." Upon closer inspection, you'll see that the lithographic stone, of considerable thickness and weight, appears to rest on a cart. This cart, guided by side rails, can move longitudinally—here, from right to left in the drawing. The stone is secured onto its iron cart, which is attached to a belt that wraps around a drum connected to the axis of the star-shaped wheel visible on the left in the background. The printing process can be illustrated by the following experiment. Take two sheets of paper. On one, draw something with a very fatty pencil. Then place this drawing against a blank sheet, as shown below:
The left hand, pressing firmly on both sheets together, simulates the "knife," visible in the pen drawing in its raised position, with its hook for gripping. Using your right hand, pull both sheets together. As the first sheet passes under the "knife," the fatty pencil on it is pressed onto the second sheet, transferring its mark.
The process in lithography is analogous. After the stone has been inked (we'll see how later), a sheet of "tank paper"—that is, high-quality, relatively thick paper made from rags—is placed on it. This paper is first moistened with water to make it more pliable. On this sheet, a felt plate is placed, followed by a thick greased leather, and finally the knife is lowered, pressed down by a mechanism not visible from this angle. Since the lithographer is expected to print, consecutively, between twenty and a hundred impressions, he cannot afford to waste time tightening with a screw. Instead, tightening is achieved by pressing a pedal, which provides a strong lever arm. The mechanism of this pedal is visible on the left, in the background. Once the pedal is depressed and locked in place, the lithographer then turns the wheel visible on the left—the wheel that gave its name to this machine. To do so, he uses his arms and, if necessary, his feet. It is crucial that the stone's forward movement be as regular as possible; otherwise, any irregularity would result in local variations in ink coverage. As soon as the stone reaches the end of its travel, the operator releases the pedal, raises the knife, quickly returns the stone to its starting position, and prepares it for another pass. To do this, he grips the sheets with small metal tongs to avoid soiling them with his fingers. His assistant will then hang them on a string to dry. Just above the signature, in the foreground, two ink rollers can be seen—used like pastry rollers.
The unresolved question is: how do we engrave these stones? First, they are polished in pairs. To do this, two heavy stones are placed face to face and rubbed against each other by hand, using sand as an abrasive. Sand and water. This process gives the stones a grain, depending on the grain size of the sand used. Coarse sand produces a rough stone, and vice versa. If we were to ink the stone immediately after removing it from the bench, it would become uniformly covered in ink. Used on the "horned beast," it would deposit an equally uniform layer of ink onto a sheet of paper.
The artist now faces the stone with a lithographic pencil, which is a very fatty pencil. Using this, he draws directly onto the stone. Drawing with a pencil means covering a sheet of paper more or less completely with an opaque substance derived from the tool's motion. Pressing hard produces a dark black line. With lighter pressure, a gray tone is obtained, gradually becoming lighter until it approaches invisibility. But what is a gray line? In astronomy, albedo—ranging from zero to 100%—measures the ability to reflect light. A "black" object is simply one with zero or near-zero albedo. A "white" object has a high albedo. A white sheet of paper reflects incident light, absorbing only a small portion. It does not behave like a mirror, because the light is scattered in all directions. The pencil lead, very black, consists of a material with extremely low albedo. By covering the paper with pencil lead, we reduce the local albedo value. In short, one can draw on a lithographic stone exactly as one would draw on a sheet of light gray paper. The grain of the stone evokes the grain of various papers available commercially: Bristol, Ingres, Canson, etc.
The lithographer, incidentally, must design his drawing "in reverse," because the image printed will be inverted. Personally, I have produced a number of lithographs of views of Paris, such as the famous Place Furstemberg. After making a conventional pencil sketch on site, I had to copy it while observing my stone's reflection in a mirror. One gets used to it (as with all engraving techniques, such as copper engraving, which I have also practiced). Once the drawing is fixed on the stone, how do we etch it? In the simplest way imaginable: with acetic acid. We apply the acid to the stone and let it act. This results in a chemical abrasion.
The chemical agent attacks the stone's raised areas first. Where it can act, it produces a smooth surface that no longer holds ink. Where the stone has been covered with a "spread" of lithographic pencil, the grain remains intact. That part, when inked, will produce a deep black. Between the two: all possible shades. What is extraordinary is that the acid's attack faithfully follows the desired gray tone. After a certain time, once the acid has done its work, the stone is washed, and all traces are removed with a solvent...