My fiance and I are having a formal, black tie wedding at a gorgeous symphony hall. We have decided that the entire wedding with be black and white and have a vintage 1920's theme - although this not a theme wedding, it will have styles from the 1920's. We have decided that we want it to be formal and black tie. I know it's polite to write "Black Tie Optional" on the invitations... but is there a way to write black tie NOT optional? While I don't mind people showing up in black suits, I would really like to get the point across that it is not a khaki -and-button down affair. How can I get my point across politely?