Firing is the final production step for ceramic products. For colored glazes, factors such as firing atmosphere, temperature, heating and cooling rates significantly affect their color development. Therefore, controlling and mastering the firing system is crucial for improving and stabilizing product quality.
Different colored glazes require different firing systems. First, kiln positioning is extremely important for the firing of colored glazes. Different areas of the kiln exhibit distinct variations in temperature and atmosphere, making proper placement essential for glazes sensitive to these conditions. Generally, the upper and middle sections of the kiln chamber have higher temperatures, making them suitable for firing copper-red glazes, crackle glazes, and transmutation glazes.
Additionally, the following points should be noted:
- Handling highly fluid glazes: For glazes with high fluidity, besides using “slag cakes” as supports, refractory clay “pedestals” should be employed. A bonding slurry—composed of 50% kaolin and 50% alumina powder—should be applied between the base of the ware and the pedestal to facilitate easy separation from kiln furniture after firing.
- Avoid mixing incompatible glazes: Glazes with different properties, such as copper-red and titanium-yellow glazes, or copper-green and opaque white glazes, should not be fired in the same sagger to prevent cross-contamination from volatile coloring elements (e.g., copper).
- Cooling requirements:
- Volatile glazes (e.g., copper-red) should be fired at lower temperatures and cooled rapidly.
- Iron-blue, cobalt-blue, manganese-red, and crackle glazes also benefit from fast firing and rapid cooling.
- In contrast, temmoku (iron-crystalline) and matte glazes require slow cooling.
- Low-temperature colored glazes:
- Glazed ceramic bodies fired in an oxidizing atmosphere typically fall into two categories:
- Lead-based glazes (e.g., Tang tri-color, vanadium-red, and Ge green): Firing range 700–900°C.
- Lead-boron glazes (e.g., chicken-blood red and peacock green): Firing range 1000–1050°C.
- Excessive temperatures dilute the color, while insufficient temperatures impair color development.
- Glazed ceramic bodies fired in an oxidizing atmosphere typically fall into two categories:
- Large-sized products:
- Heating should be gradual, and cooling must be slow to prevent thermal shock and cracking.
