If the dishwasher is vibration-free and the porcelain is arranged sensibly, there is no more risk of breakage due to high water pressure with common types of dishwasher.
The cleaning process in the dishwasher must be intensified with the addition of detergents and with high water temperature. The chemical additives must be designed so as to achieve a relatively good degree of cleaning even with hard water and in a machine that works less than well mechanically. This is often achieved by increasing the alkalinity. Detergents with high alkaline content are not only harmful to decorations but also for glass.
High rinse temperatures (over 60°C), however, not only increase the harmful effect, but can also encourage adherent deposits on the dishes. The kind of decoration plays a significant role in the longevity of porcelain when using a dishwasher. Underglaze decorations or those that have been baked into the glaze at very high temperatures are extremely resistant to all chemical and mechanical influences. Most decorations are melted at temperatures of 1220 - 1250 °C and the colours used for these are acid-proof and leave no lead residues.
Porcelain colours have also been developed with regard to their resistance to chemical detergents. Optimum durability with these contrasting chemical effects, with acid on one hand and alkaline on the other, can however only be achieved within certain limits. Nevertheless, it is a fact that almost all popular porcelain decorations show satisfactory resistance to most chemical detergents these days.
Certainly, long experience with dishwashers has shown that, for example, temperature shocks (i.e. sudden change from hot to cold water) are harmful for both decorations and glasses. New dishwashers have taken account of this experience in their design.
When buying a dishwasher, consider the following aspects.
1. The dishwasher should have a gentle programme that does not exceed 60 °C.
2. The rinse temperature in the machine must match the temperature set on the thermostat.
3. The machine may not permit any abrupt temperature differences when changing water.
4. Precise dosing must be guaranteed for detergents and rinse aids.
5. The machine must run quietly.
6. The water pressure in the dishwasher may not be so high that it can move the porcelain and glasses.
7. The detergents recommended by the manufacturer for glass and onglaze decorations must be tested.
8. The racks in the dishwasher should also allow for pitchers, bowls, pots and oval platters to be easily accommodated.
9. The dishwasher must have a water softener if you have hard water in your location.
If these conditions are met, then you can expect to get a reasonable period of use out of your porcelain, glass and cutlery without any noticeable marks on the surfaces or decorations. Changing the detergent or rinsing agent can also be crucial. It is essential to ensure that the selected agents are gentle on decorations and glass.
Are porcelain glazes or decorations affected by acidic foods (vinegar or fruit acids etc.)? This question is often asked. As our porcelain glaze is a feldspar glaze without any lead added, no lead deposits or damage to the glazed surface is possible.
The only acid that could affect the porcelain glaze is hydrofluoric acid, but this is incredibly rare in daily life and only used in certain chemical processes. This is why our undecorated porcelains, but also underglaze or onglaze decorations are completely unaffected as they are under or in the glaze and so completely enclosed and protected by it. What is known as the Lead Law (Federal Law Gazette No. 258 v. 23.12.60) protects onglaze decorations. It regulates the use of lead oxide as a flux for glazes and decorations on cooking and dining dishes. According to this law, it is forbidden to manufacture dishes that discharge more than 2 milligrams of lead per container to the respective acid after 24 hours in a 4% acetic acid solution.
To counter this risk, the decorations must be baked in at a sufficiently high temperature and acid-resistant colours used. Newly developed glaze colours also contain no lead and can therefore also discharge no lead. Only the glaze colours for red and orange tones contain small amounts of cadmium. The discharge values for these, however, are far less than the limits set by the US Food and Drug Administration, FDA, so that they also pose no risk to health. Consumers are also protected from harmful substances by the DIN standard 51032, valid since December 1977, and the applicable DIN standard 51031 Parts 1, 2 and 3. They determine that materials and items intended to come into contact with food must be checked as to whether they discharge harmful substances when in use. Certain limits are crucial here, compliance with which is constantly monitored by relevant laboratories.
You don't have to be a physicist to come across the concept of microwaves these days. The frequency range of electromagnetic waves (in between radio and infra-red radiation) is now used just as frequently for heating, re-heating and cooking food.
Families often eat at different times these days. Food has to be kept warm for a long time but taste freshly made. With microwaves, food is prepared – in microwave-safe porcelain containers – and heated quickly when needed. This is done without losing flavour. The microwave shortens cooking time. All chilled food can be brought up to room temperature in no time, e.g. butter becomes spreadable in 10 seconds.
Steamed, boiled and braised foods (fish, vegetables, stews, casseroles) cook especially well. But even pre-sealed meat dishes can be finished off in the microwave. The microwave is ideal for preparing baby, senior and diet food as less seasoning is needed and the dishes can be made with less fat.
More and more people are enjoying the benefits of microwaves. This is why the need for microwave-safe dishes is increasing. High-quality Seltmann porcelain is perfect for use in microwaves without being damaged. One thing, however, should be noted: microwaves and precious metals don't mix. In general: don't put porcelain decorated with valuable precious metals (gold, silver, platinum) into the microwave.
Customers come into our shops time and again to draw attention to what they believe are faults in their porcelain. These are so-called ‘dark stripes, scratches or cuts’ that can be seen on the glaze after some use.
The widespread opinion that this is damage to the glaze is easily refuted.
You can remove this knife abrasion very simply: use one of the liquid, non-abrasive cleaners available today, like the ones used to clean cooking surfaces, or ‘etolit’ porcelain cleaner by etol (www.etol.de).
Seltmann hard-paste porcelain is perfect for use in a salamander grill. Salamanders are used to pre-heat plates and platters very quickly in order to keep food at the optimal eating temperature for longer. The salamander is also used to brown dishes.
Hard-paste porcelain is always the best material, as it resists the fast heating and can retain heat for a very long time.
Improving the energy performance with the LfU
On behalf of the porcelain industry, Seltmann worked closely with the State Office for the Environment (LfU) to produce energy saving concepts for the Erbendorf factory in 1997 and 1998. The LfU had chosen the Erbendorf factory because it was the most advanced operation of its kind in Bavaria.
The flue gases from firing the porcelain are purified in generously sized filter systems. This not only meets the limits required by law, but also falls below them. The heat used during the porcelain firing is recovered as far as possible and used for room heating and hot water.
The Erbendorf factory invested in state of the art kilns that, in addition to their very high efficiency (less heat loss), can also adapt to fluctuating capacity needs. Between 1998 and 1999, another two million DM were invested in saving energy.
Porcelain has been known as a Chinese products ever since the heyday of West Chinese cultures (1122 to 770 BC). Porcelain was not invented in China, but is considered to be the result of a long development process. Porcelain pieces were brought to Europe from the 13th century by merchants, researchers and world travellers like Marco Polo via arduous journeys. Porcelain was only mainly imported via Holland from the 17th century. The Chinese kept a tight hold on the secret of manufacturing the then very expensive materials – we in Europe had to reinvent it.
The invention of porcelain is associated with the German alchemist and apothecary assistant Johann Friedrich Böttger (1682 - 1719). At the beginning of the 18th century, Johann Friedrich Böttger, Ehrenfried Walther von Tschirnhausen (Tschirnhaus), Freiberg Mining Councillor Gottfried Pabst von Ohain and other mining and metallurgy specialists began investigations commissioned by Augustus the Strong to uncover the secrets of making porcelain. Their efforts were a success. In 1708/1709, the team led by Johann Friedrich Böttger first succeeded in creating white hard-paste porcelain (‘white gold’).
By royal decree of 23 January 1710, the first European porcelain manufactory was founded by Augustus the Strong in Dresden and transferred to Albrechtsburg Castle in Meissen in March of the same year. Johann Friedrich Böttger was put in charge of the manufactory.
Medici porcelain, French Fritware, Réaumur porcelain, faience porcelain and many others were not true porcelain as they did not possess all the characteristics. This is why it is very difficult to ascertain which ‘porcelain factories-manufactories’ really did manufacture porcelain. When Italian majolica went out of fashion, faienceware with its white glaze and blue colours took its place.
The operations established in the 19th century in the Upper Palatinate may well also have sold faience porcelain as true porcelain, due to sales difficulties, lack of capital and mobility and other factors.
Calling a company a porcelain factory was greatly preferred to the term faience, as porcelain manufacture was very much respected by the people.
The desire to own porcelain was triggered by bowls, vases and jars brought back by Marco Polo from his travels in China in the 13th century. The history of European porcelain begins with the discovery of the manufacturing method by Ehrenfried Walther von Tschirnhaus (1651 - 1708) and Johann Friedrich Böttger. Von Tschirnhaus managed to produce the first piece of white hard-paste porcelain after years of experiments in his crucible. Previous efforts had been made by Böttger to produce gold in Albrechtsburg Castle in Meissen at the behest of Augustus the Strong, Elector of Saxony and King of Poland.
Instead of inventing gold, porcelain was born. Tschirnhaus developed focusing mirrors that were used to achieve the high temperatures. He made a porcelain cup in October 1708. After von Tschirhaus's death (11.10.1708), Böttger carried on the research into porcelain. In 1709, he managed to make red stoneware that was named ‘Böttger stoneware’ after him.
The new porcelain, hard-paste porcelain, is today being continuously improved in terms of fire-resistance (for catering facilities), chip-resistance, surface hardness, stackability and dishwasher-resistance.
Only this enables it to be used in systemware lines and large kitchens. The ‘systemware’ and ‘catering porcelain’ product groups are the result. The development of the porcelain industry up until the end of the 19th century took place in three steps.
Looking at them in the light of the results, primarily ‘luxury porcelain’, luxury goods and hand-painted figurines were made in the first period.
Simple shapes and relatively thick bodies featured in the second period, the introduction of ‘domestic ware’.
The increase in quality during the third period, featuring fine bodies, gave rise to ‘fine tableware’.
This latter is now also used to mean domestic ware.
Porcelain and the Upper Palatinate
Porcelain could not be manufactured in large quantities due to the complicated and costly production process. Its manufacture lay exclusively in the hands of the ruling princes and was inherently linked to them: on the one hand, the operation integrated into the castle was a source of income, on the other, the tableware was intended to boost his profile.
The raw materials of quartz and feldspar were easy to get hold of, but kaolin was rare and expensive at that time. In the second (mercantile period), location evaluation was the primary factor for starting a business. Operations could now be outside of castles.
Porcelain factories were generally located in places where fuel and labour were available. These two factors had a larger impact on the choice of location than relatively high-quality raw materials.
On the one hand, they could sell to whomever they chose, on the other, the businessman had to do without the prince's financial support. The third period after the war (1870) saw most factories being set up where the porcelain industry was already established or where transport connections allowed for it.
The development of the porcelain industry now took its greatest strides forward.
The first business
The porcelain industry was most widespread in terms of numbers of business in Thuringia, followed by Silesia, Sarreguemines and Upper Franconia.
As in all of the Upper Palatinate, only a few business in this sector were located in Regensburg. Various circumstances lead to the introduction of porcelain manufacture in the Upper Palatinate: the northern part of the Upper Palatinate is located between the natural resources of Bohemia and the first manufactories in Thuringia.
It was therefore only a matter of time (and capital) before the first porcelain makers settled in this region. The reason no business started up in the 18th century is because, firstly, the guilds' grip on the old imperial city was only loosened in the 19th century, and secondly, they lacked the capital. Koch, an entrepreneur, founded the first Upper Palatinate porcelain business in Regensburg in 1803, which later became known under the name of Schwerdtner. The financial problem was solved only after the arrival of Mainz Prince C. Th. von Dalberg as he looked very favourably upon this project and supported it financially. Starting a business outside of Regensburg was therefore impossible in the Upper Palatinate.
Other reasons for the establishment of porcelain production was the wealth of fuel, the kaolin deposits found in Amberg, Pressath, Kemnath and Mitterteich, as well as cheap labour. The local glass industry provided workers trained in similar tasks to the porcelain industry.
It was especially important for the porcelain industry that the manufactory was never subjected to compulsory guild membership. (The reason the establishment of the Regensburg porcelain factory may have regarded the guild system as a hindrance could be because this business was not recognised as a manufactory. This was because the living space and the workshops were in rather a modest property).
The porcelain industry was like a modern branch of trade in which manual skills never really took hold. However, it still had a long way to go to reach mass production.
Initial sales problems
The porcelain industry's main market in 1806 was the Orient, while local demand was met with faience and stoneware products. Porcelain tells the story of how an exclusive product for the few became something for everyone through industrial development and progressive reduction of production costs.
As soon as production began, it was clear that demand was low even until the middle of the century. In addition to the newness of the product, the causes were the initially fairly high prices, the low purchasing power of most people and their frugality.
The Regensburg Porzellan- und Steingutfabrik [porcelain and earthenware factory], managed by Koch, had to switch to producing stoneware 7 years after starting operation, as this sector experienced an unprecedented boom.
The combination of porcelain and stoneware factory, as you can tell from its name, allowed the company to attract a wider customer base. The benefits of porcelain over pottery were quickly recognised:
porcelain's appearance and durability triggered increased demand also amongst the general population from the 50s. It paved the way for the creation of new businesses.
The new energy source
The woods could no longer keep up with the demand for wood from the factories and their kilns. This is why the factories made themselves independent of water (water shortages in the summer months) and wood from the forests from the start.
Long-burning lignite became the basic fuel of the porcelain industry. Around this time, the Heinrich Waffler stoneware and porcelain factory came into being and stayed in existence from the end of the 1850s to the turn of the century.
At the same time, production of porcelain clay and mud underwent an extraordinary expansion (from 1856). The area between Amberg, Schnaittenbach and Freihung annually produced 10,000 tonnes, part raw material, part finished product, from the plants in Marberg and Hirschau.
Extending the processing plants would only have been possible with, as the rest of the porcelain industry demanded, a cheap source of charcoal. However, these muds later had to compete with the excellent, i.e. pure and white-firing, kaolin from Bohemia.
In the end, they could not catch up in supplying Upper Palatinate porcelain plants by the start of the 20th century.
Art becomes design
Towards the end of the 19th century, the porcelain industry's production became quantitative as well as qualitative. This meant the products of the ceramic industry entered the realms of mass consumption, though this latter was the precondition for large-scale industry.
The porcelain industry was on a sound footing as this so versatile material lost its former character as a pure luxury product. It was no longer the porcelain artist, but the designer who thought on a mass production scale who designed the porcelain:
a contemporary form for young and old that could be used in every room, was practical, also reflected more than the value of the material (and purchase price) and ‘could cost nothing’ in manufacture.
The design no longer depended solely on the beauty, but directly from the plants' manufacturing capabilities. ‘We must be able to product artistic elements’. A cottage industry developed in porcelain painting in the middle of the century. Porcelain painters like these
The manufacture of hard-paste porcelain has one of the highest levels of vertical integration of all industrially produced goods: from raw materials to the finished product, all manufacturing steps are done in one factory.
Our raw materials
The main components of our porcelain paste are: kaolin, clay, quartz, feldspar, dolomite, calcite and chalk. The high quartz content in our glazes and pastes in combination with the other raw materials produces high levels of strength and wear-resistance.
We only use natural raw materials for our pastes and glazes when making hard-paste porcelain. First, the minerals, which are usually extracted in an open-cast mine, are processed by our raw material suppliers. The necessary steps for this are generally crushing, separating out concomitant minerals, washing, sieving and drying. The process of, for example, separating out coloured minerals (e.g. iron compounds) that are not desirable in porcelain, can be very complex. Only raw materials free from concomitant minerals and that retain the same composition of chemicals and minerals from delivery to delivery can be used in our high-quality porcelain.
Preparing our hard-paste porcelain pastes
The raw materials need intensive grinding and mixing. Here, what are known as the ‘hard materials’ (quartz, feldspar, dolomite, calcite, chalk) are ground in tumbling mills together with water and grinding media. The largest mills combine several tonnes of raw materials and the grinding process for the glaze takes several days. After the grinding is completed, the plastic raw materials (kaolin and clay) are added to the hard materials and the whole mixture (the ‘porcelain body’) is intensively mixed. The raw material suspension is then sieved and passed over magnets to draw out even the smallest contamination. The suspension is then subjected to filtration in what are known as ‘chamber filter presses’.
This is where the majority of the process water is removed resulting in a paste ball with a water content of between 18% and 22%. These paste balls are the precursor for the two moulding processing of ‘turning’ (e.g. plates, cups, salad bowls) and ‘casting’ (e.g. sugar bowls, coffee or tea pots, sauce boats). In turning, the paste ball is processed into a strand in what is known as a ‘vacuum extrusion press’, which simultaneously frees the porcelain paste from trapped air using a vacuum. This creates a very malleable paste that can reproduce even the finest details of the model. When casting, water and something called a ‘plasticiser’ is used to make the paste balls into a suspension whose consistency is very like cream.
There are three basic methods of shaping porcelain: turning (shaping) the plastic (wet) porcelain paste, pressing (compressing) a powdery paste, and casting a liquid paste that can also be sped up by applying pressure (pressure moulding).
When shaping plates, a slice of porcelain paste is formed between a plaster mould and a heated, rotating steel template. The top side of the plate is formed by the plaster mould while the steel template shapes the underside. After this process, the plaster mould and the item are dried together at 60°C for around 30 minutes. Then plate can then be lifted off the plaster mould. The empty plaster mould is reused in the shaping process and dried out again so that it can re-absorb moisture from the porcelain paste.
The plaster moulds have a limited life, however. For plates with raised areas, the surface of the plaster mould no longer meets the requirements of quality porcelain after 50 cycles.
For plates with no raised areas, the plaster mould can be reused about 120 times. The item itself continues to be dried intensively, which is the prerequisite for the first firing, known as the biscuit firing, which is what now follows.
The cost of producing a press mould is very high.
Elaborate designs require significant CAD input. Turned moulds are much faster to produce in comparison to press moulds, but only have a limited life and therefore have to be constantly replaced. With pressing, the ceramic paste powder is compressed between an upper and lower mould at a pressure of about 300bar. Items made in this fashion usually do not have to be dried before the first firing (biscuit firing). In addition, no plaster moulds need to be made unlike in the turning process. This method enables the manufacture of extremely accurate plates with wide, flat rims. The reproduction of even the finest details in raised areas remains constant for the entire life of the press mould.
This is where the handle, produced in the casting process (see below), is attached to the body by hand. The cup must be intensively dried before it can go to the first firing.
The paste cylinders (‘bodies) produced during paste preparation are once again pulled into thinner paste strands in the cup making machine. These are then cut into paste pieces and formed into a cup using a steel template (inner contours) and a plaster mould (outer contours). The plaster mould and the item are then dried together at 60°C for around 7 minutes. The cup (still without a handle) can now be removed from the plaster mould. The empty mould is then reused in the forming process after being dried again. The mouth rim of the cup still needs to be rounded. All of these processes are automated, which is why the machine is called a ‘cup assembly line’.
A porous plastic is used in pressure moulding, as opposed to using plaster as a dehydrating mould like in casting (hollow castings such as jugs) or turning (plates or cups). This method is used for ‘full castings’ such as oval and rectangular platters or casserole dishes. The pressure used to press the ‘liquid porcelain’ (slip) between the two plastic halves is around 30bar. The water in the slip is squeezed out through the pores of the plastic and a filtration takes place that lasts between 30 seconds and several minutes. The item can then be removed from the mould. The mould seam (ridge) is then polished off and the item is dried. The advantages of the plastic mould as opposed to the plaster mould are a far longer life, higher accuracy of the item produced and the detailed reproduction of raised areas over the entire life of the mould.
For the casting process, the paste balls from the paste preparation (see above) are made into a slip with water and condensers. This is then poured into a plaster mould consisting of at least two parts. The plaster absorbs the water from the porcelain slip and a relatively solid layer of porcelain paste builds up in the plaster mould.
This process of continuously building up the item takes several minutes. When the desired thickness of the item has been achieved, the excess slip is poured out and re-used elsewhere in the process. The mould with the item built up on the walls is treated with warm air to harden the item. The mould can then be opened and the item removed.
After the final drying, the mould seams (ridges) on the item are polished off by hand. The empty plaster mould is dried and then re-used in a new casting process.
The heat for the dryers is usually provided by waste heat from the kilns or burners supplied with natural gas.
After shaping, the items have to be dried in order to go into the first firing, the biscuit firing. Warm air, from 40°C to 120°C, is applied to the items in continuous or chamber dryers. The drying takes several hours for dishes and can take several days for porcelain figurines.
The first firing: the biscuit firing
After firing, the paste is immersed in water and becomes no longer soft, it is somewhat solidified and highly porous. These features are essential for the glazing process which now follows.
Before glazing, all items must go through the biscuit firing, regardless of how they were shaped. In this firing, which takes around 24 hours and reaches a maximum temperature of 900°C, the porcelain paste loses its ‘plastic’ properties.
The raw materials for porcelain glazing are essentially natural minerals: quartz, feldspar, dolomite, calcite and kaolin. These raw materials are finely ground as an aqueous solution and any coloured impurities are removed. The item is briefly immersed in this suspension and the porous item readily absorbs it. The item is turned and swirled to achieve an even glaze.
After a few seconds, the glaze is touch dry and the footprint for the glost firing that now follows can be cleared of glaze by wiping. Many items at Seltmann are still hand glazed to this day, as only this method can guarantee the high quality of our products.
In this firing, the glaze is melted like glass and gives the porcelain its lustre and durable, scratch-resistant surface. What is known as the glost firing takes place after applying the raw glazing materials to the fired item. This firing takes around six hours in a modern, energy-saving furnace firing table.