Vatican smoke mystery solved

March 13: The papal conclave’s recipes for white and black smoke are a mystery no more.

Yesterday, the Vatican press office revealed the composition of the coloured smoke used during the conclave to signal the results of the voting. Earlier, a Vatican spokesman had said only that the smoke was made “from several different elements”.

Both recipes are fairly standard pyrotechnical formulas.

The white smoke, used to announce the election of a new pope, combines potassium chlorate, milk sugar (which serves as an easily ignitable fuel) and pine rosin, Vatican officials said in a statement.

The black smoke, which was used last evening and today to signal that no one in the first round of balloting received the necessary two-thirds vote of the 115 cardinals, uses potassium perchlorate and anthracene (a component of coal tar), with sulfur as the fuel.

Potassium chlorate and perchlorate are related compounds, but perchlorate is preferred in some formulations because it is more stable and safer. The chemicals are electrically ignited in a special stove first used for the conclave of 2005, the statement said.

The stove sits in the Sistine Chapel next to an older stove in which the ballots are burned; the coloured smoke and the smoke from the ballots mix and travel up a long copper flue to the chapel roof, where the smoke is visible from St Peter’s Square.

A resistance wire is used to pre-heat the flue so it draws properly, and the flue has a fan as a backup to ensure that no smoke enters the chapel.

Vatican officials closed the chapel last week for preparations, including the installation of the flue and two grey stoves that connect to it by the main entrance, across the chapel from the altar.

Traditionally, after an unsuccessful vote officials would add damp straw to the ballots to make sooty black smoke.

But confusion during the 1958 conclave, when there were several false alarms — apparently because the straw failed to ignite — led the Vatican to find a more foolproof system using chemicals.