"Most smoke is due to things not burning completely, producing tiny particles that float in the air," said Robert Krampf, a science educator, in the CBS report. "The color of that smoke depends on what those particles are made of. Black smoke is usually made up of tiny bits of carbon. White smoke is usually more complex, made up of fuel, vapor, water vapor or mineral ash."
"Unfortunately, wet straw gives you grey smoke, not black smoke," Mr. Krampf said, to CBS. "This has sometimes led to quite a bit of confusion, with people thinking that a new pope had been selected if the dark smoke was not dark enough."