Firing is a crucial step in the manufacturing of ceramics. The fired clay piece is turned into a permanent ceramic piece. This process affects the durability, colour, texture, and finish of the ceramic.
Firing is more than just reaching a target temperature. The type of kiln, the firing schedule, the atmosphere, the ceramic body, and the glaze can all affect the outcome of a firing process.
Why does the ceramic piece need to be fired?
Before firing, the ceramic piece is still weak and contains materials that haven’t been converted into the properties necessary for a strong ceramic body.
The firing process removes moisture from the piece and causes chemical reactions and physical changes to the components in the clay.
As the piece heats up, the structure forms and becomes stronger.
Since this process has a big impact on the final product, even minor variations in the firing process can lead to significant differences in the outcome.
Firing Temperature
Ceramic materials are formulated to fire at specific temperatures. If the firing temperature is too low, the resulting body could be weak and porous.
If the temperature is too high, the piece could deform, shrink too much, or develop other surface problems.
Therefore, knowing the firing temperature is important for any ceramic producer.
Temperature must also be taken in context with time. For example, reaching a target temperature quickly doesn’t necessarily mean that you’re following the best schedule.
Firing Schedule
The firing schedule defines how quickly the kiln temperature rises, how long specific temperatures are held, and how the kiln is cooled.
Different periods of heating can impact the material in different ways. By following a controlled schedule, there is time for moisture and gases to escape and for changes in the material to occur without issues.
When firing larger or more complex pieces, controlling the heating process becomes even more important since different areas of the piece could react differently as the temperature changes.
Bisque and Glaze Firing
Often there’s more than one firing involved in producing a piece of ceramics.
Bisque Firing
During bisque firing, the piece of clay is transformed into a firmer ceramic body that is easier to work with and apply glaze.
It still remains somewhat porous so that it can readily absorb the glaze.
Glaze Firing
After glazing, the piece is fired again to allow the glaze to melt and fuse to the surface and the body to reach maturity.
It’s important to remember that the glaze must be compatible with the clay body. A combination that works well at one temperature could behave differently at another.
Firing Defects
Several types of defects can result if firing conditions aren’t met correctly. Cracking can occur due to uneven drying, thermal shock, or issues in the body itself.
Warping can happen when the piece softens too much during firing or isn’t properly supported.
Glaze defects like crawling, pinholes, blistering, or colour shifts can occur.
Not all of these issues stem from the firing process. In some cases, the root cause is traceable back to an earlier stage of the production process.
Kiln Loading
The way pieces are loaded into a kiln can also affect firing outcomes.
Pieces must be spaced appropriately so that heat can circulate freely, and the glazed surfaces must be oriented in a way that prevents them from touching.
When producing large batches, the pieces need to be loaded consistently from one firing to the next to ensure that they undergo similar conditions.
Establishing a standardized system for loading the kilns can help ensure that production quality is uniform across multiple firing runs.
Recording and Improving Results
Keeping records of each firing cycle can be useful in professional ceramic production.
Information such as firing temperatures and times, kiln loads, glaze combinations, and observed defects can be tracked.
When issues arise, having a record of previous cycles helps to identify patterns and determine what adjustments might be needed.
By tracking firing data systematically, you can turn what’s often an empirical process into one that’s based on knowledge and controlled by data.
Conclusion
There are many steps in the firing process, and they’re all connected to other aspects of the production process. Material selection, shaping, drying, glazing, firing temperature and time, and kiln loading all interact and affect the final result.
By paying attention to the details of these processes, ceramic manufacturers can reduce defects, improve the consistency of their products, and make informed adjustments to their operations.