The Vatican needs to find a new Pope. To notify the world of when a new Pope is chosen, the papal conclave will communicate through smoke signal. Black smoke means they haven't found a Pope, white smoke (or "fumata bianca") would mean that there is a new Pope. So what's inside the smoke?
It's still a little bit of a mystery. A Vatican spokesperson told the New York Times that the smoke was made "from different elements". Hmm, that's not exactly helpful. Historically, the Vatican has used wet straw to create black smoke, but the problem with wet straw is that it sometime created grey smoke, which, well, can look black and white. You can imagine the confusion.
The Vatican has now moved to specific colour cartridges to create the smoke. A smoke-machine supplier told the New York Times that the cartridge probably contains potassium chlorate to create the white smoke. The black smoke probably uses the same potassium chlorate but with added dye to make it look black. Officials just place the cartridge inside a stove, ignite it and let the world see the smoke. Easy. Though I guess tweeting the news still would have been easiest. [NYT, CBS News]