Which End is Up?

Dominant Curve by Vasily Kandinsky.

Kandinsky was one of the most influential Abstract artists of the 20th century. He was a teacher of both law and later art, teaching for a number of years at the German Bauhaus. He himself claimed he became interested in abstraction after seeing one of his paintings upside down.

Clay

Klee taught at the famous art school the Bauhaus and was eventually labeled as a degenerate by the Nazis after which all of his art was removed from galleries.

Object as Communication

Suprematism, 1915 by Kasimir Malevich, Stedelijk Museum, Amsterdam

Malevich is the Father of the Suprematist movement which led to Abstraction. He considered his ultimate goal to be communication through "non-object" representation, culminating in a final "white on white" painting. He considered the conveying the feeling of a work more important than portraying an object. After the Russian revolution in 1917, he became a teacher and was quite influential on the Bauhaus artists, architects, and designers.