Conversation so far:
What was Marc doing in France in 1923?
In 1923, Chagall left Moscow to return to France.
What was he looking to do once he returned?
On his way he stopped in Berlin to recover the many pictures he had left there on exhibit ten years earlier, before the war began.
What kind of pictures he was into or did?
With all his early works now lost, he began trying to paint from his memories of his earliest years in Vitebsk with sketches and oil paintings.
What else did Marc do during those years?
He formed a business relationship with French art dealer Ambroise Vollard.

Question: What did their business consist of?
Self-contained rewrite: What did Marc and Ambroise business consist of?