Black or White: What smoke colours mean when a new Pope is chosen

In an age of digital alerts and global livestreams, the Vatican continues to announce one of its most significant decisions with a signal that dates back centuries: a puff of smoke from a copper chimney on the Sistine Chapel. But behind this seemingly simple ritual lies a surprisingly complex chemistry lesson.

As 115 cardinal-electors gather in secret to choose the next pope, all eyes remain fixed on the chapel’s rooftop chimney. Black smoke (fumata nera) means the cardinals have not reached the two-thirds majority required, 77 votes, to elect a new pope. White smoke (fumata bianca) signals success. Yet, for this symbolic act to be visible and unambiguous, the Vatican has had to modernize the process, turning to science to uphold its most sacred tradition, ABC news reported.

From wet straw to smoke bombs
Historically, white smoke was created by burning wet straw, and black smoke by burning pitch or tar. But this produced inconsistent results, with ambiguous grey smoke confusing observers and media alike. So in 2005, ahead of the conclave that elected Benedict XVI, the Vatican introduced a second stove and a chemical method to ensure clarity.

Now, when ballots are burned in the original cast-iron stove, which is about 3 feet high and 19 inches wide. It triggers a smoke-producing device in a second, modern stove. This device contains a cartridge holding five chemical "charges," which are loaded one at a time. The charges produce smoke that lasts about seven minutes, enough time for it to be clearly seen by onlookers in St. Peter’s Square.

Chemical recipes revealed
The Vatican has disclosed the specific chemical recipes used:

For black smoke: A mix of potassium perchlorate, anthracene, and sulphur, BBC reported.

Anthracene, derived from coal tar, is particularly good at producing thick, black, sooty smoke. Though effective, it's also carcinogenic, which is why it’s no longer used in fireworks displays.

Sulphur, a traditional gunpowder component, burns easily and enhances the smoke density.

Potassium perchlorate serves as the oxidizer, supplying oxygen to sustain the combustion.

For white smoke: A mix of potassium chlorate, lactose (milk sugar), and rosin (pine resin, often used on violin bows for friction).

These ingredients are safer and more environmentally friendly than alternatives like zinc dust or hexachloroethane, which can be toxic and are commonly used in military-grade smoke bombs.

Though these mixtures may sound exotic, they are essentially well-known pyrotechnic formulas, carefully chosen for visibility, safety, and tradition.

Behind the scenes: Engineering the ritual
Both stoves are connected via a joint exhaust pipe that leads to the chapel’s iconic chimney. To ensure the smoke’s successful appearance, the fuel is electrically heated and backed by air fans to keep the plume steady and visible. Vatican officials have likely tested the process thoroughly to avoid scenarios where large sooty flakes break into smaller ones, potentially changing black smoke into white midair, a known issue in bonfires.

Why not more colors?
While the current system is reliable and rooted in centuries of tradition, some observers can’t help but imagine a more colorful future. Rainbow-colored smoke, like that used in air shows and military displays, is made by adding bright pigments or dyes such as indigo and rhodamine.

Could beige smoke signal a break? Amber an impending decision? Burgundy a celebration? So far, the Vatican has resisted any such modern flourishes. For now, the ritual remains a solemn black-or-white affair, with centuries of history preserved by a precisely timed chemical reaction.

As the world awaits the next puff of smoke, it’s worth remembering that the spectacle is more than just symbolic, it’s also a triumph of science in service of tradition.