They depict landscapes and so their concentration on space, mass and volume is the thing that can be argued as Cubism. In a work such as Houses at L"Estaque, a restrained use of shifting viewpoints is combined with a rendering of forms in space in terms of a continuous pattern of flat surfaces, subdued in colour, that tilt in and out of the picture frame. These methods were taken further in paintings like The Port (1909) which provided stimulus for Picasso's faceting of buildings and sky in his Horta de Ebro landscapes of 1909. An example is Factory at Horta de Ebro. A crucial technique here called "a passage" involves the breaking of the contours defining both the things depicted and the overall faceting so the surfaces appear to flow together and blur the distinctions between solid form and space. Paintings were seen to capture both the palpable tree dimensionality of the world revealed through the eyes and also to draw attention to itself as a two-dimensional thing. Cubist paintings were both a depiction and an object themselves. From 1911, this emphasis on the status of a picture as an object was sometimes reinforced by Picasso and Braque by means of mixing sand and gesso in their paint to accentuate the unevenness and tactility of the canvas surface. Picasso was the quickest to take the implications of space, volume and mass to their extreme. In 1910 he produced pictures that so comprehensively broke down the distinction between form and space that the identity of the subject was obscured. An example is Female Nude, the work produced both produced by Picasso and Braque was characterised by difficulties in the legibility of images that arose from the decision to open form fully out into space. This kind of cubism was later referred to as Hermetic Cubism.
Early Cubism has been related to different sources. Picasso's work for example has been linked mainly to Primitivism, especially African Sculpture.