Complex sentence: Screen painting became a popular form of folk art in Baltimore's immigrant working-class communities; during the peak of screen painting in the 1930s and 1940s there were around 100,000 painted screens by over 100 artists.
Split into simpler sentences: Screen painting became a popular form of folk art in Baltimore's working-class immigrant communities. During the peak of screen painting in the 1930s and 1940s there were approximately 100,000 painted screens by over 100 artists.