The Vatican is revealing what the smoke signals emerging from the Sistine Chapel chimney are made of, after the stir caused by how much more distinct the black smoke in this conclave has been compared to the past.

The Vatican spokesman the Rev Federico Lombardi said the black smoke that came Tuesday and Wednesday - indicating a pope had not been elected - was made by adding cartridges containing potassium perchlorate, anthracene (a component of coal tar), and sulfur to the burned ballots.

The white smoke signaling a pope has been elected is produced by potassium chlorate, lactose and chloroform resin. The Vatican is burning the flares following confusion in past conclaves about smoke color.

Lombardi said that neither the chapel frescoes nor the cardinals inside suffered from the smoke.