VATICAN CITY (AFP) - The Vatican installed a special chimney on the Sistine Chapel from which white smoke will signal the election of a new leader of the world’s 1.2 billion Catholics as cardinals prepare for the centuries-old tradition starting on Tuesday. The conclave of 115 cardinal electors will be held under Michelangelo’s famous frescoes to choose the 266th pope, after the ageing Benedict XVI became the first pope to resign since the Middle Ages saying he wanted to be “a simple pilgrim” again. French cardinal Andre Vingt-Trois, the Archbishop of Paris, told AFP in an interview that there were around “half a dozen possible candidates.”