Since our website talks a lot about ceramic tile, and we correspondingly have helped a lot of homeowners get connected with the corresponding contractors, we only thought it was a good idea to also spend some time talking about what a kiln, and how it works.
These ovens are used to finish ceramics in, by heating them to desired temperatures to complete processes, drying them and causing them to become denser and harder. A range of different things are all made in kilns that range from bricks and tiles to pottery, including Raku.
They’re not new, in fact they have been around for thousands of years. Before they were first discovered, around 6,000 BC, pit firing was used.
What is a Kiln?
Kilns are an important part included in the process of making ceramics, such as porcelain tile, although not limited to it.
The exposure to the high temperatures inside the kiln will stop physical and chemical reactions. The firing will also mean that clay can no longer be recycled after having been fired. Different things will affect the way the clay finally turns out, including the preparation of it, its composition and the temperature and length of time it’s fired.
Glazes are often added to ceramics in order to make them better withstand the different elements they’re likely t be exposed to. Glazed ceramics is a lot better than unglazed in terms of water-resistance which is important if they’re event meant to be used for bathroom floors.
After the ceramics has been fired a first time, liquid glass may be added to it, and upon going back in and being fired, this will fuse with the clay. Alternatively, a sealant can be applied to ceramics, thereby better protecting the porous material against water. A third firing can be used for further decorative elements being added.
The length of the firing, the heat and the mixture of material going into it will reduce the size of the pores, making it less susceptible to water damage, but also causing it to shrink a little bit. The size of the pores, and therefore the water absorption rate is what determines if you have normal ceramics, or whether it is porcelain.
What is the Difference Between Ceramics and Porcelain?
What most people don’t know is the fact that normal ceramics and porcelain are in fact very similar things. As porcelain hasn’t been regulated, the suggested definitions come from standard groups that try to help consumers gain better insight into what it actually is they’re buying. Their definitions of porcelain have the thing in common that the material has a water absorption rate below 0.5%, meaning that when the material is lowered into water, it absorbs less than 0.5% of its own weight in the process.
A Tunnel Kiln and the Intermittent Kiln
A tunnel kiln is a long oven in a continuous form through which the ware is transported. Unlike the intermittent kiln, the tunnel kiln doesn’t have the same temperatures at the ends as it does in the middle. On the other hand, in an intermittent kiln, the clay is simply placed inside of it, and the structure is closed. The temperature is then raised to the desired level. With traditional ware, it is left to slowly cool, although Raku is taken out and cooled off rapidly.
Electric or Gas Kilns
Kilns are traditionally either gas or electricity fired, with natural gas and propane being common types of fuel for them as both types of ovens are easy to control the temperature of. The electric ones are also more common for smaller places such as schools. Although there’s no open flame, which is what helps create the reductive, gas can be introduced for that purpose.
Temperatures Used For Firing
Potters want to get that perfect color, no matter if they’re just starting out or have been working with pottery for a long time, and the temperature will affect the color of the pottery. Even if you feel like the hardest part was actually creating the creative work and shaping it, now is when it really matters.
Glazes are not created equal, and what that means is that they will melt at different temperatures, which affect the temperature you will need to ensure. Rather having the glaze fuse with the clay, it may simply run off if it becomes too warm in the kiln for that specific type of glaze. Too low temperatures, on the other hand, will not give satisfactory results either.
For typical earthenware, those made of low-firing materials, maturity is reached at 1940℉, although it can vary slightly. Cone 04 is the average that’s being used and it produces a orange-yellow color as a consequence. Earthenware is usually glazed to protect it.
Kaolin is usually what is used for porcelain, although they’re commonly mized with other types since it makes it possible to fire them at lower temperatures and still obtain the desired result, but the purity of the clay is what determines the firing temperature. The temperature range at which it does best is between 2380℉ and 2455℉, at which point it turns white. Glazing can be added to it, although the availability is somewhat limited.