White Smoke, Pope; Black Smoke, Nope: How Conclave Smoke Gets Its Color

A chemical mixture is added to the cardinals' ballots to signal conclave vote.

ByABC News
March 13, 2013, 12:26 PM

March 13, 2013— -- The world waited with bated breath for the election of a new pope, with all eyes fixed on the tiny chimney perched on the roof of the Sistine Chapel for a sign of either black smoke or white smoke.

For three votes, the smoke spewed out in thick black billows, indicating a new pope has yet to be chosen. The conclave needs 77 votes, or a two-thirds majority from 115 cardinal-electors, for a single name to elect a new pope.

Then suddenly, at 7:06 p.m., Rome time today, the smoke again appeared. And it was white. We now have a new pope.

But what gives the conclave smoke, or the "fumata," its thick, distinctive coloring is a certain chemical mixture.

Let's go back to high school chemistry class for a minute. According to the Vatican press office, the black smoke is produced by a mixture of potassium perchlorate, anthracene and sulphur.

The white smoke is a mixture of potassium chlorate, lactose and a pine resin, also known as Greek pitch.

READ: Vatican Handout on the Conclave Stoves and the "Fumata"

Here's how it works: When the cardinals' ballots are cast and counted, the ballots are burned in a two-stove system.

The ballots and personal notes are burned in a cast-iron stove that is about 3-feet high and about 19 inches in diameter. It has been used since the conclave of 1939, which elected Pope Pius XII.

When the ballots are burned in the older stove, it triggers an electronic, smoke-producing device outfitted on a second, more modern stove, which was first used in the 2005 conclave for the election of Benedict XVI.

The device releases a cartridge holding five "charges" or containers of one of the two chemical mixtures. The five charges are loaded one at a time into the device to produce enough black or white smoke to remain visible for about seven minutes.

Each of the five charges are about 25 centimeters by 15 centimeters by 7 centimeters, according to the Vatican, or roughly 10 inches by 5 inches by 3 inches -- more or less the size of a box of tissues.

The exhaust pipes of the older, cast-iron stove and the modern stove are joined together as one singular pipe, which then leads to the Sistine Chapel's chimney. So the smoke we see from St. Peter's Square is a mixture from the cardinals' burning ballots and the chemicals.