A muffle furnace (sometimes, retort furnace) in historical usage is a furnace in which the subject material is isolated from the fuel and all of the products of combustion including gases and flying ash.
Today, a muffle furnace is (usually) a front-loading box-type oven or kiln for high-temperature applications such as fusing glass, creating enamel coatings, ceramics and soldering and brazing articles. They are also used in many research facilities, for example by chemists in order to determine what proportion of a sample is non-combustible and non-volatile (i.e., ash). Some digital controllers allow RS232 interface and permit the operator to program up to 126
The term muffle furnace may also be used to describe another oven constructed on many of the same principles as the box type kiln mentioned above, but takes the form of a long, wide, and thin hollow tube used in roll to roll manufacturing processes