raise the curtain
Also, lift the curtain.
Begin or start, as in It's time to raise the curtain, guysstart shoveling.
Make something public, disclose. In this sense, both terms often occur with on, as in We won't know what the new design is until they lift the curtain on it. Both usages, from the mid-1700s, allude to the curtain raised at the beginning of a theatrical performance, revealing the stage.