In it he opened his "art store", which soon developed into the "Galerie Welz", whose first exhibitions were devoted to the works of Klimt, Schiele, Kubin and Oskar Kokoschka.
[1] Later exhibitions focused on the Vienna Secession, the Nötscher Kreis [de] (Nötsch Circle), Italian and French art of the 19th and 20th centuries, and German Expressionism.
[5][6] In 1939 and 1940, Welz acquired 26 works from the Jewish art collector Heinrich Rieger who was deported to Theresienstadt and murdered in the Holocaust, along with his wife.
[8] Welz undertook regular buying trips to Nazi-occupied Paris on behalf of Baldur von Schirach and other prominent Nazis.
[14] In 1976 Welz bequeathed a large part of his private collection, including the complete printed works of Oskar Kokoschka to the province of Salzburg.