Ceramic firing is an essential process in the creation of pottery and ceramic art. It involves heating raw clay objects in a kiln at high temperatures until they undergo physical and chemical changes that give them their final properties, such as hardness, durability, and glass-like surface. This article provides a detailed look at the entire ceramic firing process, from bisque to glaze firings, and offers tips on how to achieve the best results.
Step 1: Preparing Your Ware
Before any firing, the clay body needs to be prepared properly. This includes wedging the clay to remove air bubbles and forming it into the desired shape. Once shaped, the clay must be dried slowly to prevent warping or cracking. The drying process can take several days, depending on the thickness and size of the pieces.
Step 2: Bisque Firing
Purpose: Bisque firing is the initial firing process used to turn ‘greenware’ (unfired clay) into ‘bisque’ or ‘biscuit-ware’. This firing removes all physical water and most or all chemical water from the clay, making it porous and ready to accept glaze.
Temperature: Typically, bisque firing reaches temperatures between 1720°F to 1940°F (cone 06 to cone 04).
Process:
- Loading the Kiln: Ensure that pieces do not touch each other to allow for even heat circulation.
- Heating: The kiln is slowly heated to avoid thermal shock, and careful control of the temperature rise is crucial for even drying and firing.
Step 3: Glaze Application
After bisque firing, the ware is removed and allowed to cool. Next, glazes are applied to the bisque ware using various methods such as dipping, pouring, brushing, or spraying. Since bisque ware is porous, it readily absorbs the liquid glaze.
Step 4: Glaze Firing
Purpose: Glaze firing is where the real magic happens. The aim is to melt the glaze applied to the bisque ware to form a glassy surface coating.
Temperature: The temperature for glaze firing is generally higher than bisque firing, usually ranging from 2167°F to 2372°F (cone 5 to cone 10).
Process:
- Loading the Kiln: Care must be taken to place the glazed pieces so they do not touch, preventing them from fusing together.
- Firing Cycle: A slow heating rate is essential, especially during the initial phase to avoid glaze defects such as pinholes and blisters.
Tips for Successful Ceramic Firing
- Even Loading: Distribute the pieces evenly inside the kiln to promote uniform temperature distribution.
- Ventilation: Proper ventilation is crucial during the early stages of firing to allow for the escape of gases and moisture.
- Pyrometric Cones: Use cones to monitor the heatwork inside the kiln. These cones measure the effect of temperature and time and will bend when their respective temperature is reached.
- Kiln Shelves: Apply kiln wash to shelves to prevent glaze from sticking, which could ruin both the ceramic piece and the shelf.
Conclusion
Understanding the complete ceramic firing process is crucial for achieving high-quality finished products. Each step, from preparing the clay and bisque firing to glaze application and the final fire, plays a vital role in the outcome of your ceramic pieces. With careful attention to detail and proper firing techniques, you can maximize the beauty and durability of your ceramic creations.