Porcelain – The definition from the product knowledge of Holst Porzellan
Poetic definition of porcelain
This page is still under construction (wv-kh)
Created from sand, stones and earthen materials, shaped and shrunk and fired in the fire, the “white gold” is created. Hardly any other material offers so many different qualities under one name as porcelain. Chromium steel, copper, silver, gold and platinum almost naturally describe their difference to one another and thus create a hierarchy in the price expectations of the buyer. In the past, it was the noble names that gave porcelain its value and their name was a guarantee of high quality. Today this is different!
The Association of the Ceramic Industry e.V.: “…one hundred hands are needed to make a porcelain piece. Accuracy and conscientiousness are prerequisites for the production of valuable porcelain pieces. They are produced within the framework of a diverse, well thought-out manufacturing process. After the annealing firing in the kiln, the porcelain then receives its glaze firing at approx. 1,400 °C. During this process, the material is exposed to numerous random factors, such as the nature of the raw materials and the influence of the fire. Even today, despite the possibilities offered by machines, the design of the mould is still largely done by hand. Natural raw materials are carefully processed by human hands. This is exactly what gives the value of the products produced. Slight deviations in colour, shape and thickness are therefore possible and typical for the product…”.
Industry definition of porcelain
A proper definition of “porcelain” – which can be applied with legal certainty – is difficult, especially as there are no established industrial standards (DIN) and no corresponding monitoring bodies. Although porcelain is documented purely scientifically from materials science, in many places it is not defined in depth due to a lack of specialist knowledge and the economic significance of the industry. It may be that this circumstance is due to the handicraft origin of the production or because the use of porcelain as a foodstuff commodity is now subordinated to extremely strict guidelines.
In addition, in some countries the term ‘porcelain’ is distinguished differently from the traditional ‘stoneware’ or ‘chinaware’. In most cases this is due to a curiosity: The biscuit firing is carried out at a higher temperature range than the glost firing (high firing) – which does not deserve this name because of precisely this curiosity. Porcelain – to distinguish it from other types of ceramics – must be analysed according to its two main components: The body (as a high fired mass) and the glaze. The glaze of the porcelain corresponds in its composition to the glass and is therefore scientifically easier to define.
Although it is commonly referred to as “feldspathic porcelain”, the porcelain shards also basically consist of approximately 65 to 80% glass, in which millions of tiny mullite and quartz crystals are embedded. This explains why “real” porcelain allows a transparent flow of light. It is mainly this property that distinguishes porcelain from other ceramic materials. Feldspar – an important raw material for porcelain – is a silicate mineral that belongs to the mixed crystal family. It has a transparent rock structure interspersed with crevices and contributes to the transparency of porcelain.
Laboratory definition of porcelain
From the theory of materials – i.e. purely chemical – porcelain belongs to the group of silicate ceramics. Silicate ceramics, as the oldest group of all ceramics, has a dominant share in fine ceramic products. Essential components of these multi-phase materials are clay and kaolin, feldspar and soapstone as silicate carriers. In addition, components such as alumina and zircon are also used to achieve special material properties, e.g. high strength.
In addition to the crystalline phases, a high proportion (> 20 %) of glass phase, the essential component of which is silicon oxide (SiO2), is usually produced during sinter firing. Due to relatively low sintering temperatures, good process control and high availability of the natural raw materials, silicate ceramics are considerably cheaper than oxide or non-oxide ceramics. The latter require elaborately produced synthetic powders and high sintering temperatures.
Silicate ceramics are used, for example, in thermal engineering, measurement and control technology, process and environmental engineering, high and low voltage technology with typical applications such as insulators, fuse cartridges, catalysts, housings and in a wide range of applications in electrical installation technology. Silicate ceramics continue to be found in the refractory sector. In porcelain, the mineral phases mullite (aluminosilicate) and quartz or alumina must be perfectly detectable, and in bone china at least Ca-phosphates.
Only a combination of materials (raw materials) and a sufficient firing temperature allows “real” porcelain to be produced.
Above 1,300 °C, the glaze of the porcelain can melt out and sinter the underlying mass. Only in this way can the hardness and strength of the body, which is so characteristic of porcelain, be achieved.
Customs definition of porcelain
The customs definition of porcelain is not intended to determine the material, but rather to determine import duties based on the cost of the material and its use. The customs classification of an imitation porcelain in tariff group 69 1111 xxx does not entitle the importer to call his imitation “porcelain”! Many – and even significant – importers and trademarks in the European Economic Area are subject to this misconception. Please read about this in the section Commodities/Characteristics/Tariffing.
Why is the definition of porcelain so important?
Ceramics and porcelain have very different properties and unfortunately consumers can hardly distinguish between them when buying them. The shard of porcelain has a quasi life-long stability and is resistant to aging, corrosion, decay or damage resulting from its intended use; it is water- and acid-proof, UV- and light-resistant, non-decomposable and weatherproof, scratch-resistant, cut-resistant, ovenproof, microwaveable, dishwasher-proof and prevents the spread of bacteria and germs like no other material. The high density of porcelain gives the shard greater physical stability and better temperature storage. Porcelain keeps warm better and longer than ceramic. Porcelain is a higher quality material than ceramic – and the production of porcelain is more expensive than that of ceramic.
Porcelain is always also ceramic, but ceramic is never porcelain!