<P> The major variation from the forge and fire just described is a' back draft' where there is no fire pot, and the tuyere enters the hearth horizontally from the back wall . </P> <P> Coke and charcoal may be burned in the same forges that use coal, but since there is no need to convert the raw fuel at the heart of the fire (as with coal), the fire is handled differently . </P> <P> Individual smiths and specialized applications have fostered development of a variety of forges of this type, from the coal forge described above, to simpler constructions amounting to a hole in the ground with a pipe leading into it . </P> <P> A gas forge typically uses propane or natural gas as the fuel . One common, efficient design uses a cylindrical forge chamber and a burner tube mounted at a right angle to the body . The chamber is typically lined with refractory materials such as a hard castable refractory ceramic or a soft ceramic thermal blanket (ex: Kaowool). The burner mixes fuel and air which are ignited at the tip, which protrudes a short way into the chamber lining . The air pressure, and therefore heat, can be increased with a mechanical blower or by taking advantage of the Venturi effect . </P>

What kind of forge is used on forged in fire