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Vatican smoke signals: The science behind the smoke

White smoke indicates that a new pope has been chosen, while black smoke signifies no decision. But where does the color come from?

Members of the Vatican Fire Brigade install the chimney on top of the Sistine Chapel that will emit smoke as cardinals prepare to vote for a new pope. The conclave is scheduled to start today and will be attended by 115 cardinals. Christopher Furlong/Getty Images

To observers of the papal conclave, one part of the process will probably stand out as the most visible and exciting. Today, all 115 cardinals will isolate themselves from the rest of the world, their only contact with the outside world being smoke signals.

What the fumes indicate is simple: black smoke means there has been no decision on a new pontiff. But if the "fumata bianca," or white smoke, flows out of the chimney, then the world knows there is a new Bishop of Rome. The color has to be just right, or millions of onlookers will be fooled.

But just how does the smoke get its color?

"Most smoke is due to things not burning completely, producing tiny particles that float in the air. The color of that smoke depends on what those particles are made of," Robert Krampf, a science educator who calls himself the Happy Scientist, told CBS News via e-mail. "Black smoke is usually made up of tiny bits of carbon. White smoke is usually more complex, made up of fuel vapor, water vapor, or mineral ash."

Originally, the Roman Catholic Church burned wet straw with the paper ballots to give the smoke its dark color, which worked for a while.

"The idea behind the wet straw is to keep the fuel from burning completely. The incomplete burning produces the particles of carbon needed for dark colored smoke," Krampf said. "Unfortunately, wet straw gives you gray smoke, not black smoke. This has sometimes led to quite a bit of confusion, with people thinking that a new pope had been selected if the dark smoke was not dark enough."

To eliminate the confusion, they've now moved on to using chemical compounds to give the smoke the proper color. Along with white smoke will also be the ringing of the bells of St. Peter's Basilica to signal a new pontiff.

As CBS News' Bob Schieffer discussed on "Face the Nation," it is important that the smoke is the right color, because it's not just the locals that get confused, but the world as well.

"All eyes will soon be on that chimney again, and even in the age of Twitter, we'll all be doing what people have been doing for thousands of years, trying to read the smoke signal."

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