Vatican City, 2 May 

Preparations for the conclave to find a new pope accelerated Friday with the installation of the chimney out of the Sistine Chapel that will signal the election of a successor to Pope Francis.

Vatican firefighters were seen on the roof of the Sistine Chapel installing the chimney, a key moment in the preparation for the 7 May conclave.

After every two rounds of voting in the Sistine Chapel, the ballots of the cardinals are burned in a special furnace to indicate the outcome to the outside world.

If no pope is chosen, the ballots are mixed with cartridges containing potassium perchlorate, anthracene (a component of coal tar) and sulfur to produce black smoke. But if there is a winner, the burning ballots are mixed with potassium chlorate, lactose and chloroform resin to produce the white smoke.