During that time, his father changed the family name from Grandmontagne to Grossberg; much to Carl's displeasure.

In 1919, he resumed his studies; first with Walther Klemm at the "Hochschule für Bildende Künste" in Weimar then, in 1921, with Lyonel Feininger at the Bauhaus.

Upon completing his studies, he moved to Sommerhausen, near Würzburg, where he was married in 1923 to Mathilde Schwarz.

[1][2] Three years later, he had his first solo exhibition in Stuttgart, followed by another at the Galerie Nierendorf in Berlin and several others in Cologne and Düsseldorf.

The following year, he received a commission for a monumental wall painting, to be displayed at an exhibition called "German People-German Work".