With the inauguration of the new Catholic leader, Pope Francis I, last week, the Vatican has revealed how the coloured smoke used during the conclave to indicate the results of the vote is created.
The Sistine Chapel was closed the week before conclave to prepare for the event, including the installation of a copper flue and two stoves. The ballots are burned in the older of the two stoves and the smoke from the ballots mixes with the coloured smoke from the other stove as it travels up the flue to the roof where it is visible from St Peter’s Square. It is at this point where the Vatican’s decision is made public; black smoke signals an inconclusive vote whereas white smoke reveals a new Pope has been chosen. A chimney fan and a resistance wire are also used to ensure that the flue draws properly and that no smoke enters the chapel.
The Vatican has revealed that the white smoke is created by combining potassium chlorate, pine rosin and milk sugar. The black smoke, used only twice during this conclave, is made from potassium perchlorate and anthracene (a component of coal tar) and sulphur as the fuel. Traditionally, damp straw was added to the ballots to make the smoke appear sooty but during the 1958 conclave, a failure to ignite the straw caused confusion amongst the anticipating crowd so a better way of creating the black smoke was found.