In the world of ceramics, whether handmade or industrial, there are two types of firing:
In ceramics, whether handmade or industrial, there are two types of firing: low temperature (maximum firing at 1000ºC) and high temperature (from 1000 to 1280ºC). As we saw earlier, depending on the type of ceramic, we will have one firing or another one. This is important to have in mind, especially if you are thinking of buying a kiln and you want to make stoneware or porcelain pieces (not all kilns have enough power for high-temperature firing).
In addition to the differences in firing temperature, there are the firing stages, which can vary according to the type of clay, from one to two firings:
Clay that requires only one firing. The slip is applied before firing, once the piece has been shaped and dried. After applying the slip, it is fired at a low temperature. This type of firing is the most traditional, quickest and cheapest. To give you an example, it is the most popular type of pottery in La Bisbal d’Emporda.
The pottery we obtain from this type of firing is called terracotta.
Remember: engobe is a clay paste obtained by mixing clay and water, which is mixed with colour to decorate the piece. Engobes are applied before the first firing. They are used on both single-fired and double-fired clay, but always before the first firing.
Double fired clay
It has two stages: the first, called bisque firing, hardens the shape of the ceramic and adopts a porous texture, making it manageable for the subsequent application of the glaze. The second stage, called glazing or vitrifying, is where the heat melts the glaze that has been applied after bisque firing and closes the pores of the clay.
Generally, biscuit baking (or first firing) takes place between 960ºC and 1000ºC. Remember that the piece must be completely dry before baking to prevent it from breaking during baking.
During baking, the pieces can touch each other in the oven, so you can put pieces of crockery together, for example on top of each other if necessary. In any case, remember to place the lighter and smaller pieces on top and the heavier ones underneath.
What type of clay is used in double firing?
- High temperature clay
- Low temperature clay
The glaze (second firing) is fired at one temperature or another depending on the type of glaze and ceramic. For earthenware pieces, most glazes are fired at between 1060 and 1140ºC. In the case of stoneware or porcelain, the temperature should reach 1200-1300ºC. In the case of porcelain, the second firing can reach up to 1400ºC, but in these cases it is not possible to glaze as the colour pigment melts (it is better to opt for a third firing in these cases if we want to decorate the porcelain).
This is not a type of clay but a decorative technique. In this case, it is used to apply ceramic intaglio to finished pieces, as well as in the application of details with gold. This third firing is usually carried out at about 600ºC.
We hope we have helped you to sort out the different types of firing that exist in ceramics. When you buy the clay, glazes or your future kiln, you will see that firing is without doubt 50% of the manufacturing process, something that requires experience, trial and error and lots and lots of patience.
See you in the next post. Don’t forget to leave your comment.