Commentary by Clement Greenberg

"COLLAGE WAS A major turning point in the evolution of Cubism, and therefore a major turning point in the whole evolution of modernist art in this century. Who invented collage--Braque or Picasso--and when is still not settled. Both artists left most of the work they did between I907 and 1914 undated as well as unsigned; and each claims, or implies the claim, that his was the first collage of all...
...the task of keeping the surface at arm's length fell all the more to eye-undeceiving contrivances. To reinforce, and sometimes to replace, the simulated typography, Braque and Picasso began to mix sand and other foreign substances with their paint; the granular texture thus created likewise called attention to the reality of the surface and was effective over much larger areas. In certain other pictures, however, Braque began to paint areas in exact simulation of wood graining or marbleizing. These areas by virtue of their abrupt density of pattern, stated the literal surface with such new and superior force that the resulting contrast drove the simulated printing into a depth from which it could be rescued--and set to shuttling again--only by conventional perspective; that is, by being placed in such relation to the forms depicted within the illusion that these forms left no room for the typography except near the surface...


...When we examine what each master says was his first collage we see that much the same thing happens in each. (It makes no real difference that Braque's collage is on paper and eked out in charcoal, while Picasso's is on canvas and eked out in oil.) By its greater corporeal presence and its greater extraneousness, the affixed paper or cloth serves for a seeming moment to push everything else into a more vivid idea of depth than the simulated printing or simulated textures had ever done. But here again, the surface-declaring device both overshoots and falls short of its aim. For the illusion of depth created by the contrast between the affixed material and everything else gives way immediately to an illusion of forms in bas-relief, which gives way in turn, and with equal immediacy, to an illusion that seems to contain both--or neither."

Source:
http://www.sharecom.ca/greenberg/collage.html