Most fires involve carbonaceous fuels such as wood, paper, plastics, petroleum, or textiles. When these fuels do not burn completely because of a deficiency of oxygen, the conversion of carbon into carbon dioxide and water is impeded; and free carbon, or soot, appears as smoke. Some fuels, such as alcohols and cellulose (cotton or paper, for example), contain oxygen and tend to burn cleanly when air diffuses into the flame. Insufficient oxygen can also lead to a yellow flame because unconverted carbon particles glow yellow hot. In addition, many common materials contain some sodium or other elements that give yellow or other colors to flames. Whether a flame is light yellow, orange-yellow, or reddish depends on the temperature of the flame. The hotter the flame, the lighter the color. White or light gray smoke is usually associated with paper, straw, leaves, or wood. It is formed of pyrolysis products (gasses, liquids, and tars) that condense to form a fog of tiny droplets that bypass the flame. Other sources of white smoke include burning phosphorus, magnesium, and some other metals, but fires containing these elements in sufficient quantity are rare. Most fires will produce a mixture of black, gray, and nearly white smoke because of the variety of fuels and the variability of air supply. References or tables are not included.