What are the differences between the stoneware and the terracotta? Why is porcelain whiter than other ceramics? Which is harder? Today we explain a fundamental theme for all potters: the different types of ceramics. As we saw a few days ago, it starts with the type of mud and cooking time, but that’s not all.
Types of ceramics that every potter should know
Low temperature
Low temperature ceramics have existed for centuries. In fact, it is one of the oldest. Clay crockery, bowls, pots or pans have been made for years following this technique. They are made by hand and in large quantities to be able to offer them at an competitive price.
Today it continues to be one of the main types of ceramics, used in home, from the kitchen to the tiles. Among the low temperature ceramics, the terracotta stands out. It presents a soft, porous texture and a characteristic reddish color due to its high amount of iron oxide. This gives a great resistance to direct heat, for example in front of fire.
On the other hand, the porous texture allows evaporation through the surface, keeping the contents cool in hot environments. Now, in cold climates this type of ceramics tends to break. The reason is that porosity absorbs moisture and water, causing breakage if frost occurs.
Low temperature ceramics are usually cooked at 1.000-1.080 °C. If we add sand or chamotte to the mud, we can increase the cooking temperature and decrease the porosity. Therefore, the higher the temperature the more resistant it will be something to keep in mind if we are going to make parts for domestic use.
Stoneware
The stoneware is composed of a mixture of mud, minerals and sand or chamotte. Baked at high temperature, the density and weight of stoneware is very similar to that of a stone. It is characterized by its hardness, strength and durability, being ideal for domestic utensils or parts for the outdoors.
The usual cooking temperature is 1.200-1.300ºC, temperature that makes it impermeable to the water. You can also cook at lower temperatures and work with different oxygen ratios. In this way we can cause color differences in the ceramic, being more reddish or dark.
At the composition level, stoneware has several options. The typical stoneware is composed of 60% refractory clay, 20% ball clay, 10% feldspar and 10% silica. As more feldspar is added, the lower the cooking temperature required.
Porcelain
Porcelain is one of the most appreciated ceramic. To obtain it, we can buy an artificial mixture directly, although many artisans prefer to make their own pasta. Thus, it is possible to maintain the same mixture for all the pieces, adapted to the way of working of each potter. Porcelain paste is usually composed of 25% kaolin, 25% ball clay, 25% feldspar and 25% silica.
This mixture gives the porcelain a white color and a fine texture. In addition, it acquires a crystalline appearance, very beautiful, when it is very fine. The common cooking temperature is 1.280-1.300 ° C.
Working porcelain is not easy. There is a very narrow margin between white and dry porcelain paste. In addition, if we want to decorate it, we must work with much pamper not to break it before its cooking. Therefore, it is not usually used for domestic objects.
Raku
The raku is characterized by quick cooking. In fact, the pottery is extracted from the oven when it is red hot. For that reason it is important to work with a mud resistant to thermal contrast. The chamotte here is very important and will allow avoiding deformations, as well as adding talc. Thus, a basic mixture of raku would consist of: 50% refractory clay, 15% kaolin, 15% ball clay, 15% chamotte and 5% talc. Currently we can find mixes already prepared in the market.
This technique is very useful for making tiles and large sculptures.
What do you think? What is your favorite types of ceramics? 😉
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