We usually say “strong as iron” but in ceramics, iron is not strong at all.
Clays with a high content of iron usually cannot be fired to a high temperature because iron,
having a low melting temperature, when fired, helps to fuse the material. More often than not, clays with a content of iron can only fired to a medium temperature: 800 ˚C or 900˚C, very seldom more than 1100˚C. They have to be mixed with a refractory material to stand high temperatures.
Sora Mameby Celina Clavijo Kashu
In old times, all the process of prospecting clay, find it, clean it, test it was part of the process of making ceramics. How simplified has become now we only need to make a telephone call and have the clay delivered to our place!
Yet, as much as you handle different clays, as much as you will be looking for the “perfect” clay able to express what you feel, able to make into reality the project you have at hand.
We are not anymore involved in the process of levigation (grinding), or aging, or in the process of finding the right chemical balance of its compounds so it fires to a determined temperature or to a desired purpose, yet, we are always mixing already processed clays: sometimes we look for a nicer color, or texture, at other times we want the clay to perform safely for the user, for example when we make a casserole to bake food, in this case the clay has to stand the thermal shock that comes from taking the pot from room temperature to more than 150˚C inside the oven and out of it. Moreover, clays good for ovenware, may not be good for placing the pot directly on the flame.
But this also is not a problem: the provider has taken into account this possibility and he has prepared for you, the right clay for each purpose. To say it in more details, when you buy clay, you should verify not only the intended firing temperature but also what purpose are you going to use it for, and also, if you are going to model it with your hands (pinching or making coils), or on the wheel (throwing), or with a help of a plaster-mold (molding). Indeed, nowadays, we can enjoy wonderful clays good for any way of forming and handling, all it takes is to verify it with the provider.
2010-06-06 14:26:12
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Lola
- Very Nice
Very interesting. When you work the ceramics you have to use a particular oven to reach those temperatures, correct?
Are your works hand painted?
Thank you
Lola
2010-09-29 12:21:49
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Celina
- Lola
Yes Lola, we need special ovens which are called kilns and these develop high temperatures. Ceramics can be fired to a wide range of temperatures from 500˚C for enamels to 1400˚C for certain porcelain clays. A ceramic kiln is made with refractory bricks so can stand those temperatures.
Normal process is to fire a piece three times: the first one to around 800˚C so to allow the clay to transform into ceramics (so it makes easier to paint and glaze), the second one to around 1000 to 1400˚C so the clay vitrifies and a third time to add over glaze decoration to around 500 to 850˚C.
And yes, all my work is hand painted. Some pieces are painted before glazing and firing the piece to maturity (1250 to 1270˚C), and others are painted also after glazing & firing, to a lower temperature in what we call a third fire (800˚C).
Thanks for your interest in my work and sorry for taking all this time to answer your questions!
Celina
Very interesting. When you work the ceramics you have to use a particular oven to reach those temperatures, correct?
Are your works hand painted?
Thank you
Lola