The Ceramic Process
The basics of firing ceramics
Loading Kiln with Greenware:
When loading greenware in the kiln, pieces can touch each other. To prevent distortion, place lids on their corresponding pieces. Position the tallest items in the center for optimal heat circulation. Ensure all ware is completely dry before firing to avoid cracking or explosions. Use the SLOW BISQUE program for heavy loads with a Preheat time of two to three hours, or the FAST BISQUE program for lighter loads with the same Preheat time. Preheat overnight to thoroughly dry and start the expansion of the ware.
Venting:
If using the Vent-Sure automatic vent system, turn it on for the entire firing. If manually venting without a powered vent, keep all peepholes open initially and close the bottom ones after the low firing is complete (when red heat is visible). Leave the top peephole open throughout if no automatic downdraft vent is used. For heavy greenware, use the Preheat feature and consider propping the lid for the first hour, but be cautious to avoid cracking.
Loading Kiln with Glaze Ware:
Place pieces ½” apart to prevent them from touching and sticking during expansion. Ensure no pieces touch thermocouples. Follow similar instructions as for greenware firing. Use either FAST GLAZE or SLOW GLAZE programs or consult your glaze supplier for recommendations.
Overglaze Firing:
When firing overglazes such as Gold, Palladium, Mother of Pearl, China Paints, etc., vent the kiln up to 1100°F. If manually venting, keep peepholes open unless using an automatic vent system like Vent-Sure. Consult clay and glaze suppliers for recommended cycles.
Speed of Firing:
Do not fire the kiln as fast as it can go; follow the recommended firing cycles from glaze or clay manufacturers.
Soaking:
Hold the kiln at certain temperatures for uniformity and to smooth out glazes. Avoid long soak times at high temperatures to prevent element and thermocouple degradation. Use witness cones to monitor heat-work and manually turn off control when needed.
Firing Log:
Maintain a firing log to track times, load weights, temperatures, and results.
Applying Kiln Wash:
Apply kiln wash to the kiln floor and the upper sides of shelves to the thickness of a postcard. Apply three separate coats, ideally fired on for best results. Fire at least to cone 018—hot enough to give the kiln wash enough adherence to the shelf to prevent it from coming off in the second coating.
Bisque and Glaze Firing Stages:
- Complete Drying: Ensures all moisture evaporates before reaching 212°F.
- Ceramic Change: Water in clay crystals and minerals vents off, requiring slow firing and venting.
- Quartz Inversion: Occurs around 1060°F with a 2% particle size increase during heating and contraction during cooling.
- Burnout: Burns off organic matter at red heat.
- Sintering: Clay particles form bonds and start to lump.
- Decomposition: Clay and glaze ingredients deconstruct and recompose into glass.
- Vitrification: Achieves glassification of clay, strengthening ware before it slumps.
- Glaze Set, Cool & Freeze: Glaze and clay bond, solidify, and cool slowly to prevent crazing and heat shock.
For a detailed guide on each stage, refer to the instructions provided by clay and glaze manufacturers and suppliers. Proper use of vent systems and careful monitoring of firing processes are essential for achieving the best results in ceramic firing.
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