How is a pope chosen? Inside a conclave, with cardinals, two-thirds and white smoke

A pope is chosen by a conclave, a gathering of the College of Cardinals convened to appoint him. To vote, a cardinal must be no more than 80 years old on the day before the pope dies or resigns, and a two-thirds supermajority is required to elect. The cardinals vote in the Sistine Chapel in Vatican City and are lodged in the Domus Sanctae Marthae. The current procedures come from Universi Dominici gregis, issued by Pope John Paul II on 22 February 1996 and slightly amended by Pope Benedict XVI in 2007 and 2013.

It was not always like this. From the earliest days of the Church until 1059, the pope, like other bishops, was chosen by the consensus of the clergy and laity of the diocese. In 1059 the College of Cardinals became the sole body of electors. The word "conclave" comes from the Latin cum clave, "with a key". After the interregnum of 1268 to 1271, and concerns about political interference, Pope Gregory X decreed in 1274 that the cardinal electors should be locked in seclusion and not allowed to leave until a new pope had been elected.

Inside, the cardinals hold up to four ballots a day, two in the morning and two in the afternoon. After the ballots are burned, the smoke tells the world the result. Since 1914, black smoke from a temporary chimney on the Sistine Chapel roof has meant that no one has been elected, and white smoke announces a new pope. Since 2005 the bells of Saint Peter's Basilica ring as well. In 2013 the Vatican disclosed how the colours are made: potassium chlorate, lactose and pine rosin for white, and potassium perchlorate, anthracene and sulfur for black.

One last step belongs to the winner. The cardinal dean asks him in Latin whether he accepts his election, and there is no requirement that he say yes: he is free to answer "I do not accept". In practice a cardinal who means to refuse says so before he gets enough votes, as Giovanni Colombo did in October 1978.