In the exciting world of pottery everything is not clay and water. There is a wide range of raw materials, techniques and tools to extract and combine their properties to work. For this reason, today talk about the different clay types for ceramics and explain their secrets.
Know the clay types for ceramics
We can say that the cooking of the clay allows the production of ceramics. Normally, the temperature is 700ºC. From here, if the temperature is higher, the fusion between particles can become vitrified, achieving an even more solid and impermeable piece. But it is important to know the different clay types and the advantages of each type of cooking. This will allow us to know better how to elaborate the piece that we are looking for.
Generally, the clay is usually classified into three types or categories according to the cooking time and final hardness: low temperature, stoneware and porcelain.
To understand this, we must know what kind of pottery clay we have and how we can work it. Physically, the fusion of the particles originates in the fluxing agents in each type of clay. For example, red muds are rich in iron oxide, which allows for a solid and resistant melting at lower temperatures (around 1000 °C). In contrast, porcelain and stoneware fluxing agents are scarcer, so components such as refractories, chamotte or sand are added to achieve higher vitrification. As you can see, they are temperatures that escape the possibilities of the oven of our kitchen;).
The clay and mod
According to its geological origin, we find two types of clay: primary and secondary. The primary is much more scarce since it is in the place where it was formed. The secondary (also called sedimentary) is the result of erosion and the movement of the earth.
Starting from this base, the potters work with 2 types of mud, natural and prepared. Let’s look at the characteristics of each one.
It is the one we can use with only a minimal cleaning. The primary clay is the purest, but also the least “plastic” given the structure of its particles. Therefore, the secondary clay, subject to changes and movements, is more plastic. It should be noted that it is rare to use natural mud on its own as they are usually combined with other materials to achieve a better balance between resistance, cooking and shrinkage. This further complicates the division of raw materials, leaving as follows:
- Primary clay or kaolin: is not very “plastic”, but is the common component in clay pastes and glazes. Its vitrified version, known as moloquita, is what is used as a chamotte in many clay pastes.
- Clay ball: is the name with which it is also known the secondary clay. By itself it is very plastic, too. If it is cooked, it adopts a white color, being one of the basic elements for the obtaining of the porcelain and the stoneware.
- Stoneware: it is very difficult to find it in its pure state. In the common case, it is a mixture of secondary clay and other minerals that allow improving its quality. In the natural state it presents a grayish color, which happens to white once cooked
- Red mud surface: it is the most common among natural muds.
- Refractory mud: it is known to be used to be exposed to high temperatures. It is extracted from veins close to the coal and can be used alone or mixed with other clays. It is also usually used to obtain chamotte once cooked, ground and reduced to grain.
- Bentonite: is a mineral very similar to the ceramic that is usually added to different clay types to improve plasticity.
The mud prepared
It is an artificial mixture of natural muds and other raw materials. Refining, grinding, cleaning and impurities are eliminated before packaging and distribution. In this way, one achieves the quality and properties desired by the manufacturer, being able to offer directly for different applications or uses. Currently we can find many suppliers that offer different clay types for ceramics. Our advice is to choose those that can guarantee the same quality in the medium-long term because, over time, the deposits are depleted and it is very difficult to find others with similar characteristics.
Generally, manufacturers of prepared mud usually classify their pastas as follows:
- Porcelain: it is the whitest of all pastes, acquiring translucent tones if it is thin. The cooking index is between 1240 and 1350ºC.
- Stoneware: this is a fine clay and easy to work, especially around. Its cooking rate is between 1200 and 1300ºC.
- Material T: is a very plastic paste, whitish and with a high proportion of moloquita. This allows to create pieces resistant to the thermal shock because it withstand without problems the deformities. Therefore, it is ideal for large pieces or floors. To date, the T material of English origin is the best quality.
- Raku: ideal for molding by hand and cooking raku (temperature from 1000 to 1280ºC).
- Low temperature paste. It is sold in red or white colors and it is necessary to vitrify it if it is to be water resistant. Its cooking is around 1000-1180ºC.
What do you think? We hope we have helped you know more about the clay types of ceramic. Remember that the experience is important, as well as know the degree of cooking of each type.
We leave it here. Remember that in Labois you will find the latest trends handmade and in professional ceramics.
See you in the next post!
Of all the clay varieties, what type would contain ZERO traces or the LEAST amount of shell?