The science behind the Vatican’s colored smoke signals


Black smoke rises from the chimney on the roof of the Sistine Chapel on March 13. (Johannes Eisele/AFP)

The black smoke that announces an inconclusive papal vote is blacker and more camera-friendly than it was in antiquity, thanks to the chemist working the conclave ovens.

They've added a number of new chemicals to the smoke signals this year, Vatican spokesman Federico Lombardi told reporters today. Cartridges of potassium perchlorate, anthracene (a component of coal tar) and sulfur went into the black smoke that signaled that a new pope hadn't been chosen. The white smoke, which signals that there is a new pope, includes potassium chlorate, lactose and chloroform resin.

“Don’t expect Swiss-watch precision," Lombardi warned, but the colors are clearly more distinct than they've been in years past.

Journalists and Vatican-watchers complained in 2005 and 1978, the last two conclaves, that the color of the smoke was difficult to read. The Rev. Thomas Reese, a Jesuit expert on the Vatican, called it "incompetence" in an interview with the AP.

The church historically burned wet straw for black smoke — the water keeps the straw from burning completely, which creates carbon particles that darken the smoke. But in 2005, after complaints that wet straw actually produces gray smoke, the Vatican made its "concession to modern chemistry" and switched to a two-stove system that mixes chemically colored black smoke before funneling it to the outside world.

No word on the chemicals in the pink smoke seen near the Vatican today, which several feminist groups released to protest the church's lack of female priests.

Caitlin Dewey runs The Intersect blog, writing about digital and Internet culture. Before joining the Post, she was an associate online editor at Kiplinger’s Personal Finance.
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