TROUBLE WITH REDS is common as they are quite sensitive and often appear faded or contain washed
out areas or dark spots. Probable causes and corrective measures (where possible) are listed below.
Too thin a coating of the red glaze. Try reapplying a thicker coat and re-firing.
Overfiring. Reds are generally fired to a temperature ranging from cone 07 to cone 06. They do
not do well at greater heats. (Remember cone 06 is hotter than cone 07).
Incompatibility with other colors. Some colors (such as green and yellow) due to chemical
composition tend to make achievement of bright reds difficult. If you suspect this problem, ask
your ceramic supply dealer which glazes may be used with their reds.
Insufficient air circulation during firing. This usually results in black spots. Reds need sufficient
oxygen to mature. Try leaving peephole plugs out until true red heat (no pun intended) has been
reached.
Soaking to long at maximum temperature.
CRACKING AND CRAZING (crazing is characterized by many very fine cracks running throughout the
glaze surface) may be caused by one or more of the following reasons:
Entrapped moisture. Make sure greenware or bisque is bone dry before firing.
Internal stress due to rough handeling.
Too rapid or uneven heating or cooling (especially in heavy, thick pieces). If this occurs, then all
of the piece does not expand or contract at the same rate, resulting in stress which is released by
crazing or cracking. You can usually tell if a glaze cracjed during heating or during cooling by
carefully examining the crack. Smooth rounded, and/or sealed cracks indicate crazing during the
heating phase & sharp angular edged or separated cracks indicate too rapid cooling (possibly a
draft from opening the lid of peephole too soon). If you suspect you are firing at too fast a rate for
your ware to properly absorb the heat, the following is a useful check. Place a cone on a shelf in
the middle of the load. Put a bisque bowl over it and fire as usual. Afterward compare this cone
with the witness cone you used for the firing. If it is not deformed to the same degree, you are
firing too rapidly for the weight of the load.
Incompatible clay and glazes. Check with your dealer for compatible materials. Crazing may often
be minimized by re-firing slowly to a slightly higher temperature than that to which the ware was
previously fired.
DELAYED CRAZING (crazing which does not develop immediately but may appear months after firing)
is the result of internal stress, usually caused by too rapid cooling (which may seem very slow to the
hobbyist). Permanent internal stress combined with a small jolt
, or vibration, can check the piece months
after firing. If delayed crazing is a problem, try re-firing to the proper temperature and cooling very slowly.
Do not open the lid or peepholes during the cooling period.
KILN MAINTENANCE
You can protect your kiln and add many extra years to its life by using this maintenance guide.
Before each loading:
Visually check kiln and its furniture.
Remove glaze spots on shelves, posts, kiln bottom or kiln sidewalls.
Clean kiln by removing ships and dust. A vacuum cleaner works well for this purpose.
Check kiln shelves for cracks. Do not use cracked shelves. Sand any rough spots and
recoat. Keep a smooth layer not over 1/16” thick. Kiln wash built up with a thick layer
may damage kiln floor by pitting due to differential thermal expansion. Do not coat
bottom of shelf with kiln wash.
WARNING
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