Loading and Firing Low-Fire Greenware
Low-fire greenware has a firing range from cone 06 to 02. The greenware must be bone dry before firing. Otherwise, it will crack or even explode during firing. Check for dryness by touching to cheek or the inside of a wrist. Ware will be cold if not dry. Another indicator of moisture is patches of darker color in the clay.
Handle greenware carefully. Cradle the pieces from the bottom. Do not lift by a rim.
Low-fire greenware pieces do not stick together during firing. Therefore, greenware may be stacked so that it touches each other. Place small items around larger ones. You can also place light greenware pieces inside larger ones. This is called nesting. Be sure that there is plenty of room for expansion inside the larger pieces. Pack nested pieces lightly so that heat can still circulate freely around each piece. Black rings in the fired ware indicate that the nested pieces were packed too tightly to burn off all the carbon.
Greenware does not need stilts. Fire ware in the position in which it will be used when finished, except for large pieces with flat, vertical surfaces such as wall plaques and clocks. These should be fired flat to prevent warping. Pieces to be used together, such as a box with its lid, should be fired in place to ensure a good fit. You can also stack mugs and bowls rim to rim.
Low-fire greenware firing is simple. Just be certain the greenware is fired to the pyrometric cone recommended by the clay supplier. If the greenware is not fired hot enough, the piece will absorb moisture after it has been glaze-fired, causing the glazed surface to crack. This is called “crazing” and is most often due to underfired greenware. To help eliminate crazing, fire greenware at least one cone hotter than glaze, and even hotter if glaze can still be applied easily to the hard bisque. While glaze may be applied to greenware and fired once, separate firings produce better quality, so we do not recommend single firing of greenware and glaze.
Allow the kiln to cool to room temperature before opening the lid.
Greenware and Glazed Ware In the Same Firing The clay is fired in two separate firings: the greenware, or bisque, firing, and the glaze firing. Greenware should not be fired in the same load as glazed ware. Not only do the two types of ware mature at different temperatures, but gases from the greenware can discolor the glaze and also cause glaze bubbles.
If you must fire greenware and glaze pieces in the same load, place the glazed pieces in the bottom of the kiln and the greenware pieces on a shelf above.
Arnold Howard Paragon Industries, Inc.