The difference between porcelain and ceramic

We are always asked where the difference between ceramics and porcelain is and we would like to answer this question for you. But we have to go back a little and get to the bottom of the origins of both materials. Let's start with ceramics. Ceramics are made of clay and are created when it is fired at more than 1000°C. So clay is the material, but what is clay?

Clay is a weathered rock and is therefore an inorganic (non-biological) material. Mountains and mountain ranges that were formed millions of years ago were eroded by wind, ice, water and other external seasonal influences. In the course of time, sand, gravel and clay have been formed. The clay particles are smaller than 2 µM (= 0.000002 cm) and look like scales or platelets under a microscope.

It is easy to imagine that clay is a diffuse material and by no means a "single-variety" material. During decomposition, various rock compounds are dissolved and remixed. Thus, layered silicates such as kaolinite and illite meet quartz and calcite and form what we understand as clay. Over millions of years, metallic compounds, the oxides, are also deposited. The different colors are the result of these inclusions. Red clay contains a lot of iron, it is basically rusted. Black clay contains a lot of manganese - also known as manganese dioxide. Don't worry, during firing, the manganese is firmly bound in the ceramic and thus no longer a cause for concern.

The firing temperature of ceramics is up to 1300 °C, but it can be divided into two upper categories. The low fired iridescent ware (earthenware and raku ceramics) and the high fired sintered ware (stoneware and porcelain). At a firing temperature of up to 1100 °C, stoneware is referred to as earthenware in ceramics. These ceramics are characterized by splendid colors, but have the disadvantage of not being waterproof. For most decorative ceramics, waterproofness is not of interest.

For vases, however, and especially for consumer ceramics, this is an important criterion. Who likes it when the cup loses its precious coffee at breakfast? The reason for this is the quartz contained in the clay, because it only melts out at temperatures above 1100 °C. In this way, quartz compresses the ceramic from the inside out, or not.

The second firing stage of the ceramic is found from 1100 °C to 1300 °C. Here one speaks of stoneware ceramics. Stoneware ceramics is characterized by its venerable earthy colors. The sound of this ceramic reminds of bronze bells. In contrast to stoneware, stoneware is absolutely waterproof, because the quartz contained in the clay could melt out.

Now to porcelain. It is very rare that clay weathers by type and if it is made of kaolin, porcelain earth is produced. This is the purest and highest quality form of clay. You will notice that porcelain consists of clay. What is the difference between ceramic and porcelain?

Porcelain has a very low content of foreign matter and consists almost exclusively of kaolin and quartz. The proportions are approximately 50 % kaolin, 25 % quartz and 25 % feldspar. In the porcelain clay, the quartz content is particularly high at one quarter and gives the porcelain its special properties. By comparison, in ceramic clay (as in utility ceramics) the quartz content is significantly lower at around 10%. The quartz is like an exchange material in clay and stretches the rock portion - the fired mass becomes transparent. This is also a sign of high-quality porcelain: it is translucent, almost like milky glass. This is exactly what the quartz does, it becomes glass! Unlike ceramics, porcelain can be fired at temperatures of up to 1500 °C. At these temperatures the glass (=quartz) in the clay melts completely and becomes transparent. The higher the clay is fired, the more resistant it is. While stoneware is relatively sensitive to cutlery, stoneware and especially porcelain are hardly affected. Even acids (acetic acid in salads, lemon in tea) cannot harm stoneware and porcelain.

If porcelain and ceramics are almost the same, why does porcelain cost so much more? The processing is the problem. Ceramic clay is relatively easy to handle and most of us had contact with it in elementary school. Porcelain is completely different here. The consistency and texture is a peculiar cross between chewing gum and toothpaste. One can easily imagine that this mass is not or very difficult to work with on the turntable. Built-up, figurative work as in decorative ceramics, are not possible with porcelain. The secret lies in casting porcelain. A viscous mass is prepared and poured into the corresponding plaster moulds. After a while, the mass is poured out again and an approx. 5 mm thick layer of porcelain remains at the edge - the secret of mass production. Mass production and then expensive? To make porcelain translucent, you need a maximum thickness of 3 mm, and this is where the proverbial chaff is separated from the wheat! With such thin walls, the walls tend to collapse or tear when drying (because there is not enough material) due to the rounding.

This is the high art of porcelain processing and this craft costs, because it takes decades of practice.

The difference between porcelain and ceramics is therefore the firing temperature! This can be selected particularly high, due to the high quartz content in the pure porcelain earth. This makes the ceramics on the one hand very robust against use, and on the other hand milky translucent.