Black Smoke, White Smoke: How the Vatican Signals Decisions on a New Pope

Once the cardinals close themselves off in the Sistine Chapel so that voting on the next pope can begin, eyes outside turn to a chimney poking out of the chapel, clearly visible from St. Peter’s Square in Vatican City. It will release a plume of white smoke if a pope has been chosen, and black smoke if no candidate has won the required two-thirds majority of votes.

It’s a tradition that scholars date to the 19th century, when conclaves were held at the Quirinale Palace, the papal palace across town that is now home to the Italian president.

In “Behind Locked Doors,” a 2003 history of papal elections, Frederic J. Baumgartner wrote that the first evidence he found of smoke being used as a signal in a papal election was from 1823. The cardinals’ ballots were burned in previous conclaves, he wrote, but there was no record that the smoke was intended to inform the outside world of a new pope.

The smoke comes from the burning of the ballots, as well as any notes that the cardinals have taken, which are placed in a cast-iron stove after each round of voting. (One round is held the first day, and four each day from then on, with two in the morning and two in the afternoon.) The ballots are burned after two rounds of voting, unless a pope is chosen.

Until this century, wet straw was added to the stove to create the smoke’s white color. But it wasn’t always reliable.

As The New York Times reported, during the 1958 conclave, white smoke seemed to appear twice during the second day of voting. That created confusion because, in fact, a pope had not yet been selected.

A Times reporter described the frenzy outside St. Peter’s: “Dozens of newspapermen in the square made a dash for the nearest telephone,” and guests at a wedding inside the basilica dashed outside, “leaving the bride and bridegroom alone in front of a priest at the altar.”

But it was a false alarm. The confusion in that conclave, which elected Pope John XXIII, led to conspiracy theories that another cardinal had been the real winner.

In 1978, cartridges were first used to enhance the black or the white color of the smoke during the conclave that elected John Paul I. When he died suddenly 33 days after he was elected, the cartridges were used again in the election that year of his successor, John Paul II.

That method was also imperfect science. In the case of John Paul I, an amusing video from the time shows beffudled reporters panicking as white smoke from the chimney turns black. “You can’t understand anything,” one frazzled reporter screams into a telephone. The Vatican later announced that a pope had been elected.

Come 2005, when John Paul II died, a more reliable system was devised that remains in use today. An electronic control unit resembling a stove is now placed alongside the cast-iron stove — they share a chimney flue — to burn cartridges that color the smoke from the ballots.

Massimiliano De Sanctis, a fireworks expert, customized one of his fireworks machines for the Vatican, and it was used for the 2005 conclave that elected Benedict XVI and the 2013 conclave that elected Francis.

“We didn’t invent anything new,” he said in an interview. “It’s the system used for fireworks.”

The black or white smoke cartridges are placed in the unit, and when the ballots are burned in the cast-iron stove, a cardinal presses a button to set off the cartridges in the unit, coloring the smoke. For each vote, six cartridges are used, and the smoke lasts about seven minutes, Mr. De Sanctis said.

After the confusion of the past, the Vatican doesn’t take chances: Once white smoke comes out of the chimney, bells will begin pealing from St. Peter’s Basilica, calling other churches in Rome to ring their bells as well.