A carburizing flame can be likened to a car engine running rich. At air/fuel ratios less than 14.7:1, not all the gasoline is burned. A similar principle applies with oxy/gas welding. Acetylene's chemical makeup is C2H2, and incomplete combustion will produce an excess of carbon-thus the term carburizing. It is also a blue and white flame with a feathered end but may have orange highlights in the outer feather, depending on how much excess acetylene there is. However, it has two inner cones. Its inner cone is also light blue but is larger than a neutral flame. A larger, light green cone surrounds the inner cone.