Explain the black and white smoke during the Pope election

Beginning in the early 1800s, the ballots used by cardinals were burned after each ballot to indicate a failed election. The lack of smoke instead signalled a successful election. Since 1914, black smoke (fumata nera) emerging from a temporary chimney installed on the roof of the Sistine Chapel indicates that the ballot did not result in an election, while white smoke (fumata bianca) announces that a new pope has been chosen.

Prior to 1945 (when Pius XII changed the form of ballot to use unsigned ballots, first carried out in 1958), the sealing wax on the complex type ballots illustrated above had the effect of making the smoke from burning the ballots either black or white, depending on whether or not damp straw was added. Until the 20th century, sealing wax customarily had beeswax mixed into its composition. The use of wax made solely from animal fat does not give as much white colored smoke, as does wax that includes beeswax. In the 1939 conclave there was some confusion over the smoke color, which was even more apparent in the 1958 conclave. The lack of sealing wax on the ballots explains the confusion over the color of the smoke in the 1958 conclave. The Siri thesis was based on the confusion over the smoke color on the first day of that conclave.

Since 1963, chemicals have been added to the burning process to augment the smoke's black or white color. Beginning in 2005, a successful election is also accentuated by bells ringing at the appearance of the white smoke.

During the 2013 conclave, the Vatican disclosed the chemicals used to color the smoke—the black smoke comprises potassium perchlorate, anthracene, and sulfur; the white smoke is composed of potassium chlorate, lactose, and pine rosin.