Vatican Unveils Secrets of Smoke

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

Art collectors of ArtKabinett social media network are always interested in the physical chemistry of colorful compositions.

The Vatican press office revealed the chemical makeup of the colored smoke used during the conclave to signal the results of the voting.

Earlier press releases had said only that the smoke was made “from several different elements.”

This week's recipes are fairly standard pyrotechnical formulas, as released by Church authorities:

The white smoke, used yesterday to announce the election of Francis I, combines potassium chlorate, milk sugar (which serves as an easily ignitable fuel) and pine resin.

The black smoke, which was used Tuesday evening 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 during the election of Pope Benedict

The stove sits in the Sistine Chapel next to an older stove in which the ballots are burned; the colored 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 preheat the flue so it draws properly, and the flue has a fan as a backup to ensure that no smoke enters the chapel.