“We do not listen closely enough to what painters have to say. They say that the painter is already in the canvas, where he or she encounters all the figurative and probabilistic givens that occupy the canvas. An entire battle takes place on the canvas between the painter and these givens. There is thus a preparatory work that belongs to painting fully, and yet precedes the act of painting. This preparatory work can be done in sketches, though it need not be, and in any case sketches do not replace it. This preparatory work is invisible and silent, yet extremely intense, and the act of painting itself appears as an afterward, an apres-coup (“hysteresis”) in relation to this work.
What does this act of painting consist of? Bacon defines it in this way: make random marks (lines-traits); scrub, sweep, or wipe the canvas in order to clear out locales or zones (color patches); throw the paint, from various angles and at various speeds. Now this act, or these acts, presupposes that there were already givens on the canvas (and in the painter’s head), more or less virtual, more or less actual. It is precisely these givens that will be removed by the act of painting, either by being wiped, brushed, or rubbed, or else covered over. For example, a mouth: it will be elongated, stretched from one side to another. For example, the head: part of it will be cleared away with a brush, broom, sponge, or rag. This is what Bacon calls a “graph” or a Diagram: it is as if a Sahara, a zone of the Sahara, were suddenly inserted into the head; it is as if a piece of rhino skin, viewed under a microscope, were stretched over it; it is as if the two halves of the head were split open by an ocean; it is as if the unit of measure were changed, and micrometric, or even cosmic, units were substituted for the figurative unit. A Sahara, a rhino skin: such is the suddenly outstretched diagram. It is as if, in the midst of the figurative and probabilistic givens, a catastrophe overcame the canvas.
It is like the emergence of another world. For the4se marks, these traits, are irrational, involuntary, accidental, free, random. They are nonreppresentative, nonillustrative, nonnarrative. They are no longer either significant or signifiers: they are a-signifying traits. They are traits of sensation, but of confused sensations (the confused sensations, as Cezanne said, that we bring with us at birth). And above all, they are manual traits. It is here that the painter works with a rag, stick, brush, or sponge; it is here that he trows the paint with his hands. It is as if the hand assumed an independence, and began to be guided by other forces, making marks that no longer depend on either our will or our sight. These almost bling manual marks attest to the intrusion of another world into the visual world of figuration. To a certain extent, they remove the painting from the optical organization that was already reigning over it and rendering it figurative in advance. The painter’s hand intervenes in order to shake its own dependence and break up the sovereign optical organization: one can no longer see anything, as if in a catastrophe, a chaos…”
Deleuze – The Diagram, in The Logic of Sensation p 81-82