Trouble Shooting
Part of the fun of what we do is share the magic of ceramics, how
bisque + glaze + kiln + an artist’s imagination can create
heirlooms and precious treasures.
But what about when it’s bad magic and produces results that
are not pleasing as opposed to “happy accidents” ?
While we would love to be able to prevent all mishaps, understanding
the whys and hows they come into being will help you diagnose and
hopefully, prevent problems in the future. Like everything else
though, a certain amount of failure should be expected. We nor our
materials are perfect all the time. Fortunately, many CCSA suppliers
offer free technical support. If you need to call, you will be asked
a variety of questions and may be requested to send your piece into
the lab for further testing. Some questions or information requested
might be:
1. Did you get a good fire?
The fact that you set your digital controller to cone 06 does not
insure that is what your kiln did. We recommend that you use self
supporting witness cones in every fire. Witness (shelf) cones are
used in a series of three:
• Guide Cone is one cone cooler than the desired temperature.
• Firing Cone is the cone temperature desired.
• Guard Cone is one cone hotter than the desired cone.
Use cones in each fire and on every shelf. If you simply cannot
use all three sizes, use the firing cone on every shelf, preferably
two. Keep a record of your results and you will discover your kiln’s
personality- hot spots, cold spots, etc. By using witness cones
and verifying that your kiln fired successfully and the desired
cone was reached, one important variable will be eliminated as a
problem source.
2. What type of glaze was used?
Knowing the type of glaze that was used and how it was applied may
give us a clue. Have the lot number available (the manufacturer
can tell you where to look) so that we can reference our records
to see if we have had any other complaints.
3. What does the surface look like?
Holes, bare spots, fine lines? Following is a description of the
problem, possible causes and potential solutions:
 Bare
Spots in glaze surface:
called crawling.
Problem 1:
Often caused by dirt, dust or oil, prohibiting glaze
from adhering to the ware.
Solution:
Make sure piece is clean before painting by wiping with damp (not
wet) sponge. Make sure hands are clean of oils, hand lotions,
etc.
Problem 2 :
Too heavy of an application.
Solution:
Lighten application. Lighty touchup bare spots and refire.
 Small
holes in glaze:
called pinholing.
Problem:
Underfired bisque is continuing to mature during glaze firing,
causing emission of gasses and interrupting the glaze surface.
Solution:
Bisque should be fired to 03-04 and glazes two cones cooler to
prevent ware from reheating and releasing gasses. Sometimes repeating
fire can smooth the glaze.
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 Large
Pinholes: also called craters, fisheyes or bubbles.
Problem:
caused by gases escaping during firing due to
a. underfired bisque
b. firing glaze while wet
c. ware not fired hot enough or piece was fired/cooled too fast.
Solution:
a. Bisque should be fired to shelf cone 04 or hotter. Two cone
difference between bisque fire and glaze fired necessary.
b. Allow glazes to dry 24 hours prior to firing.
c. Fire glazes to shelf cone 06 or recommended cone. Glazes need
an even steady ramping of temperatures and cooling. File down
craters, reglaze and refire.
Glaze rolls back: called flip back
Problem:
a. Glaze was applied too heavily, without sufficient drying time
between applications.
b. Piece was fired too wet.
c. Oil or grease on piece
Solution:
a. Allow glaze to dry between coats, apply thinner coats.
b. Allow piece to dry 24 hours before firing.
c. Make sure surface of bisque is clean of dust; wipe down with
damp sponge. Sometimes flip backs can be corrected by sanding
down, reapplying color and refiring.
 Fine
lines in glaze surface after firing: called crazing
Problem:
Generally caused by glaze and body fit problem. When talking technical,
will be described as a coefficient of expansion problem.
Solution:
Use mature bisque. Some glazes, especially non-toxic
formulations, are more sensitive to application.
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 After
firing, glaze falls off pieces:
called shivering
Problem:
Incompatability between ware and glaze.
Solution:
Coefficient of expansion. Body shrinks at a different rate than
the glaze, causing the glaze to fall off. Be very careful as the
pieces of glaze can be quite sharp. Some glazes, particularly
non-toxic glazes, are not as accommodating of less than perfect
bisque.
Gloss glaze is matte
Problem:
Glaze did not reach maturation during firing.
Solution:
Use witness cones to make sure proper fires are achieved. Refire
piece.
 Piece
cracks in kiln: called “a mess”
Problem:
a. Thermal shock or expansion of two or more glazes
b. Too heavy of glaze in bottom of piece.
Solution:
a. Use same type of glaze inside and out when glazing. Recommended
to use gloss glaze inside pieces, even when mattes are used on
outside.
b. After rolling glaze on inside of piece, invert piece to drain
excess glaze.
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