Clay and ceramics, terracotta and earthenware, stoneware and porcelain - the world of ceramics is full of terms that are not so easy to grasp. But there are big differences in the quality and durability of the products. So time to shed some light.
Out of the ground and into the kiln
The origin of the word ceramic already gives some information about the raw material and the production method. The term derives from the ancient Greek word keramos and designates products made and fired from clay.
Today there are many ways to make ceramics. This includes the construction technique with the hands, turning on the potter's wheel, casting in plaster molds or industrial production with highly efficient machines. However, all of these types of making are based on the same pattern: the clay is first prepared, brought into the desired shape and then fired in a kiln or pit.
Photo (C) Paulo Castro Photography
It all depends on the right clay
The manufacturing process of ceramic products begins with the extraction and processing of clay, the basic material of ceramics. Clay is a predominantly inorganic material that consists of fine-grained clay minerals such as silicates, quartz or metal oxides and can be plastically deformed if the water content is sufficient.
The precise composition of each clay alone determines its future use and the quality of the products. For example, some ingredients make the clay more plastic and therefore easier to work with, while others ensure good resistance to high firing temperatures. Not every clay is equally suitable for processing on the potter's wheel. And while one type of clay can withstand very high temperatures in the kiln, another will deform into an unsightly lump.
High temperatures and why they are so important
Above all, the temperature in the kiln has a decisive influence on the later end product and its qualitative properties. Because the higher the firing temperature, the more resistant the ceramic becomes. And it is also the temperature that divides ceramics into its sub-terms: A distinction is made between earthenware - which is fired below the sintering limit - and sintered material which is exposed to temperatures above this limit.
Sintering is a chemical process that starts at temperatures above 1150°C. The crystalline structures of the clay on the surface melt together and the pores close, which means that the ceramic absorbs almost no water, even without a glaze. This process is roughly comparable to the production of glass, although the visual appearance of sintered ceramics is not always distinguishable from low-fired ceramics.
Terracotta and earthenware
The category fired below the sinter limit includes earthenware and reddish-brown terracotta. The latter is easy to identify mainly because of its color and is familiar to many when using flower pots. And this is also one of the advantages of this low-fired ceramic: Due to its high porosity, the material absorbs a lot of water and then slowly releases it back to the plants. This is a decisive advantage, especially in warmer regions. However, caution is advised in winter in temperate climate zones, because frost can crack the porous material.
Earthenware also has advantages despite its porosity, which is why it is still often found on the market. Due to its high lime content, the clay is easy to work with and the manufacturing process is significantly cheaper than stoneware or porcelain due to the lower firing temperatures, which usually has a positive effect on the price.
However, tableware made of earthenware is less impact-resistant and durable than sintered ware. In addition, it must be covered with a glaze in any case, because the material itself is not completely waterproof. Earthenware is often sold as dishwasher safe. However, the unglazed base of the plate, small cracks or damages in the glaze can sometimes be problematic. Soaking in the sink or a long wash cycle in the dishwasher allows small amounts of water to penetrate and the material becomes soaked. If the ceramics are not carefully dried in the air after washing, mold can form.
Sintered ware - stoneware and porcelain
The category of sintered ware includes both stoneware and porcelain. Both types of ceramic are fired at temperatures above the sintering limit of 1150°C and therefore absorb almost no water, even when unglazed. They are easy to care for, particularly impact-resistant and therefore very durable.
Unfortunately, stoneware and some types of earthenware can hardly be distinguished visually, if at all. Both sub-types of pottery are made from a light gray or soft beige clay and are often covered with colorful glazes. It is therefore important to inquire about the material before making a purchase. Stoneware is much more robust and can usually be cleaned in the dishwasher without any problems.
Photo (C) Paulo Castro Photography
Porcelain, on the other hand, is easier to distinguish. The composition of the clay contains a high proportion of kaolin, which means that the material is very light in color and has a thin-walled and often slightly translucent appearance. Classic porcelain is often white or - if the clay was colored with pigments before casting - pastel colored. It is usually additionally coated with a transparent glaze. Because porcelain clay is rare and fired at particularly high temperatures, it is also known as white gold. Its special feature is therefore usually reflected in the price.
Spoilt for choice
Ceramics is a broad term that can be divided into porous earthenware and water-impermeable sintered goods (stoneware, porcelain). The differences in quality, ease of care and price are mainly due to the manufacturing method, the composition of the clay and the firing temperatures.
Each ceramic subspecies has certain advantages and disadvantages. Terracotta and earthenware, for example, impress with their low price. Stoneware and porcelain, on the other hand, are particularly easy to care for and durable. Which tableware you ultimately decide on should therefore be carefully considered.