 After being demobilised in 1919, he started studying painting at the Burg Giebichenstein Academy of Arts and Crafts, where he was a student of Professor Erwin Hahs (1887–1970).During this period, he formed strong and lasting friendships with fellow students Paul Zilling (1900–1953) and Helmut Schröder (1910–1974).In 1927, both Müller and Helmut Schröder joined a class taught by Charles Crodel, newly appointed to Burg Giebichstein as professor for painting and graphics.