FIRING FOR BEST RESULTS
• Don’t try to hurry the firing or cooling of your ware. It can absorb and release heat only so fast without damage to the ware.
Slow heating and cooling rates add quality and minimize crazing, cracking and breakage problems. Let the kiln cool at
least over night, then crack the lid and let pieces cool until they may be handled with bare hands. If this suggestion is not
observed you will put permanent stress in your pieces making them weaker and more subject to breaking and crazing.
• Watch firings closely to protect from overfiring. Firing too hot will damage fine detail and fade colors.
• Keep the inside of your kiln free from dust and chips, which cause imperfections in pieces. A vacuum cleaner is useful in
this regard.
• Always fire only bone dry ware.
• A cone plaque containing three cones (guide cone, firing cone, and guard cone- see section on pyrometric cones) is often
useful as a monitoring and warning device. Always place witness cones uniformly at an 8 degree angle from vertical.
RECOGNIZING FIRING FAULTS
Blotchy bisque is likely to be caused by stacking too compactly, not allowing for sufficient air circulation during firing which
results in uneven firing. Try loading more loosely and refiring.
Warped bisque
may be due to one the following causes:
• Overfiring.
• Placing ware too close to the elements.
• Stressing delicate area by improper support.
• Removing ware incorrectly from the mold.
Failure of glaze or underglaze to adhere to the ware
(crawling glaze) can be attributed to one of the following causes;
• Dirty bisque surface. Dust and skin oil are the most common offenders. Try to clean, recover and refire the ware.
• Damp bisque. Allow to dry completely, then reapply and refire.
• Underfired or overfired bisque. If underfired, refire to proper cone, then reapply glaze and refire. Overfired bisque becomes
too hard to absorb the glaze media.
• Too thick a coating of underglaze.
• Incompatibility of glaze and/or underglaze and ware.
• Your ceramic supply dealer can best advise you on clays and glazes that are compatible (expand and shrink at the same
rate and do not chemically ruin each other.)
Puddling and rippling of glazes is caused by applying an excessively thick coating of glaze. If this effect is not desired,
merely coat pieces more lightly on future ware.
Dropping glazes on vertical surfaces is caused by overfiring glaze and by excessive glaze thickness.
Shiny surface on a mat or textured glaze can be attributed to overfiring. Also textured glazes are often applied too thinly. If
this is the case. reapply and refire to the proper cone.
Cloudy appearance can be caused by dirty brushes, by placing the piece too close to the elements, by too heavy an appli-
cation of glaze, or by placing pieces too close to one another in the kiln, resulting in cross contamination.
21
To Next Page
Loading...