text: Historically, small muffle ovens were often used for a second firing of porcelain at a relatively low temperature to fix overglaze enamels; these tend to be called muffle kilns.  The pigments for most enamel colours discoloured at the high temperatures required for the body and glaze of the porcelain.  They were used for painted enamels on metal for the same reason. 
  Like other types of muffle furnaces, the design isolates the objects from the flames producing the heat (with electricity this is not so important).  For historical overglaze enamels the kiln was generally far smaller than that for the main firing, and produced firing temperatures in the approximate range of 750 to 950 °C, depending on the colours used. Typically, wares were fired for between five and twelve hours and then cooled over twelve hours.