Proscenium. That’s what you call the stage opening, and there is usually a decorative frame around it to frame the stage. And a curtain that fills the opening is called a proscenium curtain. At the centuryold ZCBJ Hall outside Du Bois, the proscenium is framed with ornate wood. The opening has been empty for a long time. The proscenium curtain, a large flat painted canvas, was rolled up and set as…