A timely explainer from Philip Ball:
The smoke comes partly from the burning of ballot papers in a special stove in the chapel. But to colour it white or black, this smoke is mixed with that from chemical additives burnt in a second stove. Traditionally the Vatican produced the different colours by burning wet straw for white and tarry pitch for black.
Anyone who has ever made a bonfire knows that damp grass will work for the former; the less responsible of you will know that chucking old tyres or roofing felt into the flames will turn the smoke black – and what’s more, noxious, because it is then full of sooty carbon particles that can clog the lungs and are potentially carcinogenic.
It’s not concern for the environment that has led the Vatican to change its ways, however. Rather, the smoke in some previous elections came out an ambiguous grey, prompting the decision for the last conclave in 2005 to use a more reliable method based on chemical ingredients.
The Vatican has now revealed what these are. For black, it uses a mixture of potassium perchlorate, anthracene and sulphur; white comes from potassium chlorate, lactose and the conifer resin called rosin, which is also used to lubricate violin strings. We needn’t imagine a team of Vatican chemists labouring like alchemists to devise these magic recipes, because what they really show is that the Vatican is making plain old smoke bombs.
(Screenshot from the site www.istherewhitesmoke.com)