Vatican conclave: Why the black smoke, the white smoke and other curious facts around just how a pope is elected

The famous smoke - black for an inconclusive vote and white to signal a victor - is created by a mix of chemicals

Members of the fire and rescue service affix the chimney onto the roof of the Sistine Chapel (Reuters)

As the world waits with bated breath to find out who the next leader of the Catholic Church is, all eyes will be on the 6ft-high copper chimney fixed on the roof of the Sistine Chapel.

Cardinals locked away in the Chapel will vote four times a day and ballots will be burned at the end of the morning and afternoon sessions - each time producing a distinctive black and white smoke which will alert the world's 1.2billion Catholics whether a pope has been elected.

The famous smoke - black for an inconclusive vote and white to signal a victor - is created by a mix of chemicals. The intensity of the colour of the black smoke this year has already caused a stir.

[Related: Black smoke signals no new Pope]

The Vatican uses a mixture of potassium perchlorate, anthracene and sulphur to produce black smoke and potassium chlorate, lactose and rosin for white.

Two stoves are used - one to burn the ballots and the other to burn the chemicals. The smoke from both mixes in a common pipe and wafts out of the famous chimney.

But this technique had not always been in place. Historically, white smoke was produced when the ballots were burned with wet straw and pitch was used to create black smoke.

The Vatican started to introduce chemicals to colour the smoke in 1963 but the system was not perfect and grey smoke confused the faithful. In 2005 the bells of St Peter's Basilica were rung to accompany the white smoke and will ring again this year.

The smoke is not the only ritual peculiar to the papal conclave. Here are five more interesting facts...

  • The word Conclave originated from the Latin "cum-clave" meaning literally "with key". The 115 cardinal-electors are locked in the beautiful Sistine Chapel every day until a successor is chosen. The tradition started in 1268 when after three years of deliberating the cardinals still had not agreed on a Pope and frustrated Romans took matters into their own hands. They locked up the cardinals and cut their rations - pressuring the men to make a decision.

[Related: Papal conclave at the Vatican - in pictures]

  • Pope John Paul II was the first pope to specify the conclave be held in the Sistine Chapel. In the past the secretive meetings have been held in Roman churches and even in Venice. This was not the only change he made. Until 2005, cardinals slept on hard beds in makeshift "cells" close to the Sistine Chapel. But the former pope commissioned a five-storey, 130-room guest house for the cardinals to sleep in.

  • Three sets of robes and shoes are prepared for the newly elected Pope in small, medium and large. Papal tailors Gammarelli, who have served the Pope for 200 years, prepare the three sets of vestments which include the white skullcap and red leather shoes. The pope dresses alone in the Room of Tears - so called because many new popes have been overcome by emotion by their election. Dressed in the red and white garments, the pope then steps out onto the famous balcony overlooking St Peter's Square, to address the crowds below.

  • While predecessor Pope Benedict XVI was the first pontiff to tweet, the Vatican is not welcoming to modern technology. Jamming devices in the Sistine Chapel will block all communications to prevent leaks. This can provide challenges - in 2005 a miscommunication meant the white smoke did not emerge in time with the ringing of the bells at St Peter's. Vatican officials frantically tried to reach the bell ringer by mobile phone to co-ordinate the two symbols - but the jamming device prevented the call from being made.

[Related: Inside the Vatican: Behind the scenes at the 'chaotic' Rome institution]

  • The voting system is complex. Each cardinal writes his choice on a piece of paper inscribed with the words "Eligo in summen pontificem" ("I elect as Supreme Pontiff"). Folding the paper twice, the cardinal carries it to the altar and drops it into the chalice. Once all the votes have been cast, the ballots are mixed and counted. One of the scrutineers calls out the names of those cardinals who have received votes. He then pierces the ballots with a needle, bundling the paper on a single thread and burning them in the stove.