Escher (1898-1972). Major themes in Escher's work are contrast, duality, transformation, infinity and spatial paradoxes. He uses symmetry to order this world of duality and paradox. This idea influences his work, both formally and psychologically.
In 1922 Escher visited the Alhambra palace and saw the wall tilings of the Moors. He was excited to find other artists who had been captivated by tilings, but also made this revealing comment: "What a pity their religion forbade them to make graven images." Escher's notebooks soon became full of repeating patterns inspired by the Moors. Imagery gave his patterns a different psychological character from the serene designs of Islam.
While Escher's work includes representation, it is still involved with the language of visual symmetry and order.
Escher was also fascinated by the concept of infinity, which led him into explorations of space beyond the two dimensional plane. He carved the surface of this six inch ball with twelve identical fishes to show that a "fragmentary" plane could be filled endlessly. When you turn this ball in your hands, fish after fish appears in endless succession.
Escher pursued themes of transformation in works he called "Image Stories" which involved images transforming from one state into another. In another version of "Pessimist and Optimist", he explains, "... on a gray wall, these human figures increase their mutual contrast toward the center ... each kind detaches themselves from the wall surface and walks into space ... Thus going round they can't help meeting in the foreground ... the black pessimist keeps his finger raised in a gesture of warning, but the white optimist cheerfully comes to his encounter, and so they finally shake hands."
"The structural world of Escher's art is fundamental to his language of symmetry ... his work ultimately refers to space and time ... [and] more than just a light hearted game ...[it] approach[es] something that is primeval and eternal, a groping for the secret of existence, much more than just filling the plane"
M. C. Escher:"ESCHER on ESCHER Exploring the Infinite",
Published in 1989 by HARRY N. ABRAMS, INC., New York
As cited at: http://www.dartmouth.edu/~matc/math5.pattern/lesson7art.html