In addition to impression, the Impressionists used the word 'sensation' to describe what they saw and painted. In French, 'sensation' is related to the verb sentir which means 'to feel'. The two words were used interchangeably by critics and the artists. Paul Cezanne claimed 'To paint after nature is not a matter of copying the objective world, its giving shape to your sensations.'
The Impressionists' study of open-air light effects led them to question the accepted conventions of local colour. They noticed that every object's local colour appears modified by reflected colours from surrounding objects. Rather than painting the colours they had learned objects to be, the Impressionists tried to put down only the colours they actually saw.
Cezanne's commitment to what he actually saw resulted in paintings that contain apparently faulty observations if viewed in terms of conventional notions of perspective. His Still Life with Plaster Cupid (c.1894) in the Courtauld collection is perhaps the most striking example of this 'faulty' vision. It is one of the most complex of his late still lifes. Cezanne dispenses with the idealisations of perspective in this painting in order to paint what he sees. He recorded how his eyes looked down at different parts of a scene from different angles. The plaster cast of Cupid, which still exists in Cezanne's studio in Aix-en-Provence (Southern France) appears larger than life. The apple in the background, apparently placed on the distant floor, appears as large as the fruit on the table in the foreground. There are further ambiguities in the relationships between the objects, such as the back edge of the table which seems to disappear into the floor. The Impressionists recognised how contrasts of colour temperature - warm and cool colours - could be used instead of purely light-dark tonal contrasts to create a sense of form in space. Distinction between prominence and recession in Cezanne's Still Life with Plaster Cupid is conveyed through a system of patches of warm (advancing) and cool (receding) colours.
Cezanne's L'Etang des Soeurs, Osny (c.1875) demonstrates the sheer range of Impressionist technique, which varied from artist to artist and during different periods in an artist's career. In the mid 1870s, both Pissarro and Cezanne made extensive use of the palette knife to apply paint to the canvas. Cezanne uses the knife in this picture to establish a series of strong diagonal rhythms in the foliage. It has also been used to form the trunks of the trees in the foreground. Green is the dominant colour and Cezanne uses varying shades and tonal contrasts to convey the play of sunlight through the trees.