After each voting session, ballots are burned. If the vote is inconclusive, a chemical substance is added to the paper to produce black smoke. Billowing from the roof of the Vatican Palace, the smoke is a message to the crowds watching in St. Peter’s Square that the church is still without a pope.
When the college eventually reaches the final decision, each cardinal lowers a purple canopy over his chair, leaving the elected Pope’s canopy folded. The final ballots are burned and their white smoke signals a successful election.
– A Papal Succession Primer
Coincidence or a signal to the faithful?