UNDER FIRED
ca: COCCIÓ BAIXA
es: COCCIÓN BAJA
Under firing is when the ware being fired does not reach the correct heat. This can be caused by the kiln not working properly or a product not being correctly prepared.
Bisque: It is very difficult to know when it is under fired, but if sounded it will be flat and the color might be different from other pieces, so if in doubt, fire it again. If it is decorated and then fired, as the clay will continue shrinking and the glaze won’t, this will cause faults in the glaze, making it matte and cracked.
Glazes: if under fired a piece will have a matte surface and if fired again to the right temperature it will vitrify correctly. This can be caused by something wrong with the elements inside the kiln or with the products being used. Sometimes a fired piece can be half matte and incorrectly fired. If this occurs, cover it with a thin layer of glaze and re-fire it at the same heat. The transparent glaze, when crude, has an uneven surface but when fired it will integrate and leave a shiny surface. With modern industrial tiles there are many problems one being that when they are decorated and fired to the correct heat they are matte, which gives them the appearance of being under fired. Read more about: Tile Problems
