We talked to Chris Mocella, coauthor of Chemistry of Pyrotechnics, to see if he could shed light on what is done to create that heavenly hue. (Take a look inside the Vatican.)

There are two ways to create smoke, Mocella explains: combustion, which produces smoke when materials are partially burned, and vaporization, which occurs when solid materials are heated to turn them first into a liquid and then into gas. "The smoke that you see when you burn wood or straw in the fireplace is from a combustion product; the carbon-heavy material in the wood burns, but not completely." This releases carbon dioxide along with "ashy" compounds that appear gray or black. In vaporization, "a solid substance is