Firing temperatures for low-fire and high-fire clays
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In this post, rather than going into exact temperatures and firing curves (these vary for each clay body and you should always check the technical data sheet or ask your supplier), what we want is to clarify a few concepts you often ask about.
Above all, because the firing schedule for a low-fire earthenware clay has nothing to do with that of a high-fire stoneware, for example.
Low-fire clays (e.g. terracotta)
Bisque firing
A typical bisque schedule would be:
- Increase by about 100 °C per hour up to 500 °C.
- From there, increase by about 150 °C per hour until you reach the temperature recommended by your supplier.
Important:
Even if it sounds counter-intuitive, low-fire clays are often bisque fired to higher temperatures than the bisque for high-fire clays and porcelains.
Low-fire bodies contain a lot of organic material. Firing hotter in the bisque helps burn out that material more completely, so later the glaze firing tends to give better results, with fewer pinholes and imperfections.
Because of this, with low-fire clays it’s quite common that the bisque firing is hotter than the second (glaze) firing, which is something that does not usually happen with high-fire clays such as stoneware, porcelain and similar bodies.
(As always, check the data sheet for your specific clay.)
Glaze / glaze firing (low-fire)
Low-fire glazes are usually fired around 1050–1080 °C (lower than high-fire clays).
A typical schedule is:
- Start by increasing 100 °C per hour up to about 450 °C.
- From there, you can switch to the kiln’s maximum ramp speed until you reach the target temperature.
High-fire clays and porcelains
Bisque firing
For high-fire clays and porcelains, the bisque does not need to go as high as in the terracotta example above.
High firing (glaze firing)
For the high (glaze) firing, a common pattern would be:
- Increase by about 100 °C per hour up to roughly 450 °C.
- From there, you can fire at full speed until you reach the temperature recommended by the manufacturer, usually somewhere around 1200–1300 °C.
With high-fire clays and porcelains, it’s the glaze firing that is hotter than the bisque, not the other way around.
Remember:
All of these values are approximate guidelines. You should always:
- Check the technical sheet for your clay body, or
- Ask the manufacturer or supplier directly.
We hope this helps to clarify some of your questions. It’s a huge field, full of exceptions. And remember: many potters work with only one type of clay (low-fire or high-fire), and there’s absolutely no need for you to master every possible case.
Another exception is third firing / overglaze. After a high-firing, once the piece is already glazed, you might choose to add a decal (the so-called overglaze / third-firing decals) and do a third, low-temperature firing to fix it.
In short: there are a thousand different situations. The best approach is to simplify and focus on the specific situation you have in front of you right now, instead of trying to control every hypothetical case.