Objects made in the furnace require the tempering process.
Once modeled, the product is placed in a dedicated oven to cool very slowly. This prevents the object from breaking as it hardens. The concept called "tempera" describes this procedure. This process, even if it may seem banal, is a very delicate phase, since, based on the size and the shape of the object, the cooling times must be corrected, otherwise the work will be lost.
Furthermore, since the object is introduced when it is still malleable, there is a risk that it will deform, therefore it must be placed on dedicated supports in such a way as to avoid this inconvenience.
When the kiln contains a permanent box-like structure heated by an external source so that neither flame nor direct heat from electric elements can impinge on the material being heated, it is konwn as a muffle kiln and the box is known as muffle.