Before World War I Bronstert visited and finished the superior school for engineers in Hagen.
These contacts led to the foundation of the group of artists „Der Fels" (The Rock) which was later completed by Reinhard Hilker and Carry Hauser.
Past the war he settled in Hagen and made contact with the group around collector Karl Ernst Osthaus especially with Christian Rohlfs.
Bronstert’s art developed from radical expressionism of the early twenties to a realistic phase and finally to a reformed impressionism as the artist claims himself.
The possibility to work as an artist without financial pressure was the reason behind Bronsterts refusal to market himself.