White smoke traditionally signals that a papal conclave has elected a pope.
During a conclave, cardinals vote in the Sistine Chapel, and ballots are burned after voting. Chemicals are used with the burning ballots to make the smoke appear black when no candidate has been elected and white when the required result has been reached. White smoke is followed by the announcement of the new pope from Saint Peter’s Basilica.
The smoke is intended as a public signal for people gathered in Vatican City and watching around the world. It is not itself the formal announcement; the senior cardinal deacon later presents the elected pope with the traditional “Habemus papam” declaration.
Modern conclaves also use bells to reduce uncertainty about the smoke’s color. The Sistine Chapel’s artistic decoration therefore serves as the setting for a continuing constitutional and religious procedure, not merely as a museum backdrop.