VATICAN CITY (Reuters) - The Vatican revealed on Wednesday the science behind the smoke signals that tell the world whether a pope has been elected.
In the 2005 conclave that elected Pope Benedict, the color of the smoke was sometimes various shades of grey, leading to confusion.
This time, the two emissions of smoke so far have been a billowing black that left no doubt that the cardinals secluded within the Sistine Chapel had failed to elect a pope.
The Vatican said the black smoke was produced by a mixture of potassium perchlorate, sulfur and anthracene, which is a component of coal tar.
The white smoke that will eventually announce to the world the election of a new pontiff, will be produced by a mixture of potassium chlorate, lactose, and a pine resin which is also known as Greek pitch.
Two stoves have been installed in the frescoed Sistine Chapel where the cardinals are voting and both are attached to a single copper flue leading up to the roof.
One, made of cast iron and used in every conclave since 1939, will be used to burn the cardinals' ballots.
The second stove is an electronic one with a key, a red start button and seven tiny temperature indicator lights. Charges measuring about 25 cm x 15 cm x 7 cm (10 x 6 x 3 inches) are electronically ignited inside it to send out either white or black smoke for around seven minutes.
To improve the draught, the flue is pre-heated with electric current and a fan helps whisk the smoke upwards.
In the 2005 conclave, the Vatican said the great bell of St. Peter's Basilica was to have rung along with the white smoke to assure the waiting crowds that a pope had been elected.
But the person on the roof of St. Peter's Basilica refused to ring the bell for about 15 minutes because he had not received the order directly from his superior.
A book about the Vatican said he received the order from a Swiss Guard and was afraid it might be a hoax.
Reporting by Philip Pullella; Editing by Alison Williams