Smoke talks. It can comfort, inform, warn - or spoil the evening for the neighbours. Whether it rises from the stove in the cottage or from the most sacred chapel, it always says something.

The eyes of the world these days are on a single chimney and the smoke that will rise from it. At the Vatican, 135 cardinals are in the process of electing the new head of the Catholic Church. Whether they have succeeded in choosing a successor to Pope Francis will be announced to the world by the smoke rising from an inconspicuous pipe protruding from the roof of the Sistine Chapel.

White smoke? We have a pope.
Black smoke? The Cardinals haven't picked yet.

Two-tone signalling is iconic today - but surprisingly young. It only officially came into use in the 20th century as the answer to a simple question: "Has he been elected yet?" People used to wait for an official announcement or a cannon shot. Nowadays, the sight of smoke is enough.

How does it work?

After each vote, ballots are burned in a special stove. To announce how the election went, the cardinals add mixtures to the fire to create coloured smoke. If no one is elected, a black smoke mixture is used. If the election is successful, a white smoke mixture is used.

But it wasn't always so clear. In the past, wet sawdust, pitch or wet straw were tried - but these often produced grey smoke, causing confusion and conjecture. So in 1978, after one election, the cardinals added chemicals to the ballot papers - the smoke was white, but some of those present were poisoned by it.

It was not until 2005 that a second stove was installed in the Sistine Chapel: one for tickets, the other for controlled smoke mixtures. And since then, it has finally been working.

A little chemical insertion (do not try at home)

The Vatican uses potassium chlorate, anthracene and sulphur to create black smoke. The moment the new Pope is elected, white smoke rises from the chimney above the Sistine Chapel - the result of mixing potassium chlorate, lactose and rosin. All in carefully measured quantities so that the smoke shows up exactly as it should - and doesn't smoke up half the Vatican.