Dirty bisque surface. Dust and skin oil are the most common offenders. Try to clean, recover and
re-fire the ware.
Damp bisque. Allow to dry completely, then reapply and re-fire.
Underfired or overfired bisque. If underfired, re-fire to proper cone, then reapply glaze and re-fire.
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 the 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 re-fire to the proper cone.
CLOUDY APPERANCE can be caused by dirty brushes, by placing the piece too close to the elements,
by too heavy an application of glaze, or by placing pieces too close to one another in the kiln, resulting in
cross contamination.
CLOUDY APPERANCE OF A TRANSPARENT GLAZE can be attributed to overfiring. Also textured
glazes are often applied too thinly. If this is the case, reapply and re-fire to the proper cone.
DISCOLORED GLAZES are often caused by one of the following reasons:
Contamination of glaze by chemicals in the ware.
Dirty brushes.
Loading pieces too closely, causing cross contamination of glazes by fumes or bubbles.
Placing pieces very close to the kiln elements, creating hot bands across the piece due to the direct
radiation from the elements. This can leave a band of slightly faded glaze across the piece.
Overfiring. Too high a heat will frequently cause colors to fade.
Glazes applied directly to the greenware.
Incompatibility of colors.
PINHOLES, BUBBLED GLAZE AND CRATERS may be attributed to one of several causes:
Immature bisque. If your bisque is not fired hot enough to complete the vitrification and remove
all vapors from chemical reactions that come from the ware, they may erupt into the glaze and be
trapped.
Dust on the ware or in the kiln.
Firing too rapidly.
Cooling too rapidly. Craters are sometimes formed by cooling the ware too rapidly, which freezes
the crater formed when the glaze bubbles. You can try merely re-firing to minimize the effect of
these defects, or you may apply a thin coat of glaze and re-fire to the proper cone which may
correct the problem.
FADED DECALS are usually due to under or over firing. Check the manufacturer’s recommendations and
re-fire underfired ware to the proper cone.
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