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The fascinating world of porcelain production

Basically, porcelain consists of three simple components, and yet the production, processing and finishing separate the simple from the special. On this page, we show you the steps our products go through, the craftsmanship required, the manufacturing methods and the processes used to decorate and finish our porcelain. You will discover that the production of white gold is not only an extremely complex and long process, but also that it still involves a great deal of craftsmanship and manual labour, despite the most modern production facilities. But above all - and this is what has distinguished our products for more than 140 years - it is thanks to the know-how, passion, attention to detail and wealth of experience of our 700 employees that each individual Rosenthal product is designed to impress with a very special formal and functional quality as well as white quality that makes your home unique.

Know-How and Passion


Our collections are manufactured in our porcelain factories "Rosenthal am Rothbühl" and "Thomas am Kulm". We have some of the most modern production facilities in the porcelain industry worldwide and, thanks to forward-looking investments, enable sustainable and resource-saving manufacturing.

But the best technology is worth nothing without skilled craftsmanship. Despite all the modernisation and automation, a large part of the manufacturing process is still done by hand: each production step - shaping, drying, firing, glazing, glaze firing, decoration and decor firing - requires special craftsmanship and technical know-how. Porcelain production is one of the industrial production processes with the highest vertical range of manufacture. And it is our passion.

700 people work at Rosenthal to create beautiful and functional products that are made with passion and attention to detail.

Rosenthal am Rothbühl factory, designed by W. Gropius

Porcelain production

Design and modelling

Rosenthal has been working for many decades together with renowned designers and artists in designing new products. A development division, which operates independently of production, known as the Creative Centre is in charge of the design evolution process from the first model through to the finished, decorated service. The Product Development Division with all its necessary workshops develops new creations for the Rosenthal, Rosenthal meets Versace, Thomas Hutschenreuther and Arzberg brands.


The work of the modellers

Modellers manually construct plaster models in close cooperation with the designers, which can be processed in every conceivable way. Round, symmetrical models are shaped from solid cylinders of plaster on the potter's wheel. Reliefs are engraved into the finished models. The modeller carves handles and spouts separately from plaster blocks. Since porcelain shrinks by approximately 12.5 % during firing and, while still hot and soft, sags somewhat through its own weight, the plaster models have to be made larger. Bulbous shapes, handles and spouts must be shaped at a steeper angle. As the degree of sagging cannot be calculated, a large amount of expertise and intuition are required.

Synthetic resin and plaster casting moulds

Once the delicate plaster moulds have been shaped to satisfaction, they are used to make the master moulds in a durable synthetic resin or in silicone. These are used in turn to make the negative plaster casting moulds. Plaster is used because it is porous and absorbs the excess moisture from the porcelain clay. A plaster casting mould can be used about 140 times. However, if the shape is in relief, the casting mould can only be used around 70 times.


Photo: First design drawings by Sebastian Herkner

Preparing the raw material

Hard-paste porcelain body is primarily made up of kaolin (50 %), feldspar (25 %) and quartz (25 %). These raw materials are crushed in large drum mills with added water and flint until they are finely ground and mixed. This liquid mixture is passed over a magnetic belt, which extracts iron particles, which would otherwise cause brown stains on the fired porcelain.

A fine mesh screen removes all other impurities. Most of the water is removed by a hydraulic press and a vacuum press sucks out the air. Now the porcelain is ready for moulding. Rosenthal is one of very few manufacturers who still produce porcelain body and glaze according to a secret formula

Production

Turning

The porcelain clay is portioned into relevant sizes and placed onto the plaster casting moulds for the cups, which are then inserted into the cup machine, a continuous moving track. A metal template is lowered and by turning shapes the inside of the cup.

Once the piece has dried, it shrinks from the plaster mould. The rough edges are trimmed with wet sponges until they are nicely rounded, smooth and even. The cup handles are cast separately. all casting marks are carefully removed by hand before the handles are attached to the cup.


Photo: Jolleying of mugs on the machines

Isostatic press moulding

Isostatic dust-press moulding of plates is another method. This involves a porcelain paste consisting of minute spray-dried granules. These granules are poured into the press mould and bond under high pressure. The press tool required is divided into two parts, the upper and the lower die. The upper die is used to shape the top of the item and has to be rigid. The lower die shapes the back of the item and is fitted with an elastic membrane to isostatically mould the pieces. When the upper and lower dies are closed, the granules are pumped into the hollow area inside using compressed air. The item is moulded under pressure of approximately 280 bar, thereby ensuring it is evenly bonded. Dust-pressed items have to be smoothed off around the rim only. The normal finishing process follows after that. Press moulding is a high efficient method and among its many advantages is a significant quality improvement in the production of plates and platters.

Slip casting

Porcelain items like teapots, handles, spouts, boxes, oval platters and figurines are shaped in plaster moulds. A porcelain slip is used for this purpose, the addition of a little water and other thinning ingredients making sure it can be poured. The two- or multi-sectioned plaster moulds absorb the water from the slip leaving an even layer of set clay on the mould wall, which is known as the body. Any remaining liquid slip is then poured out. Handles, spouts, cup feet and lid knobs are made separately and then attached to the actual body by hand, using the slip as a locating medium. Porcelain figurines are also assembled by hand from many separately cast pieces. The casting seams, visible on all pieces once the mould has been opened, are smoothed by hand with blades and sponges.


Photo: The plaster mould is filled with the liquefied porcelain paste, known as the slip.

Press casting

This method is used in the production of square and oval platters. The porcelain slip is pumped into a two-part, porous plastic mould and then put under pressure. The water escapes through the open pore canals of the plastic mould while the porcelain paste stays within. When finished, the mould opens automatically and a suction pad lifts out the pieces.


Photo: The cast and still very soft body leaves the plaster mould for the first time.

Firing

Biscuit Firing

After the raw porcelain has been pre-dried and biscuit fired at about 950 ̊C, it is no longer water soluble but still porous and water absorbent.

Glazing

The biscuit fired pieces are stamped with the logo of the company and then glazed. The glaze is immediately removed from the foot of the plates and the rim of the cups with wet sponges to prevent the porcelain from sticking to the base during the second firing. The glaze is a mixture of quartz, feldspar, some kaolin and a high proportion of different thinning agents. Because of its high content of quartz it produces a very hard surface when fired. With particularly delicate pieces (e.g. »Magic Flute« and Limited Edition Art), the glaze is applied using a special spraying process. The glaze melts when fired and fuses with the body before its pores close, creating an inseparable bond between the porcelain body and glaze.

Glost firing

In the glost firing process at temperatures of up to 1400 ̊ C the paste shrinks and becomes watertight. This causes vitrification, turning the substance into a hard, delicate, translucent porcelain. This process effects a chemical change in the porcelain item and also changes its contours. After glost firing, the porcelain is 12.5 % smaller (shrinkage) than when it was moulded. Even glost firing is done using a burn-off method nowadays in modern fast fire kilns or roller kilns.

Porcelain types

Hard porcelain

After the biscuit and glost firing processes, the porcelain is hard, impact resistant and translucent. Hard porcelain has the highest scratch resistance to stainless steel cutlery and is unaffected by acids, except hydrofluoric acid. Porcelain is weatherproof and does not change after the last firing, no matter how old it gets. It is suitable for use in the microwave oven with the exception of items decorated with precious metals (gold, platinum). The white colour of the porcelain is achieved by reduction firing. This means it is fired in an atmosphere of reduced oxygen.

Black porcelain

Black porcelain is a special Rosenthal product. As precious a porcelain as “porcelaine noire” should never be put in the dishwasher. It is best to wash it by hand in warm water and to dry it immediately with a soft cloth. Sustained contact of crockery with food containing lemon or acetic acid should be avoided as staining could occur. Black porcelain should also never be used in the microwave oven.

Processing and sorting

Grinding

The unglazed feet of the plates and contact surfaces of the porcelain are still rough even after the second firing. By grinding and polishing repeatedly they become smooth, pleasant to touch and dirt resistant.

Sorting

The undecorated porcelain, also called finished white ware, is carefully sorted by highly skilled personnel. The intrinsic characteristics of the materials and the ceramic production process, especially the firing, inevitably cause tolerances and minute deviations between individual pieces. The sorting process accurately separates out the items with such levels of deviation and discards altogether pieces with defects.

Decorating and finishing

Decorations

Through their colours, decorations on porcelain enliven the white of the material. A vase or a dinner service, richly decorated in gold, is an elegant and stately embellishment for formal occasions, whereas the same pieces decorated with a colourful floral pattern assume a friendly and cheerful character. Moreover, a variety of decorations appeal to different consumer tastes. Hence the Product Development Division offers a whole host of decorations created by renowned artists, using the strictest criteria in selecting the best designs.

Interesting facts

Aside from hand painting, there is a wide range of high-quality decorative methods available today. Artists' designs are scanned into a computer and reworked by an elaborate software programme in order to make them fit onto each piece of a dinnerware service so that they can then be transferred onto the three-dimensional shape. The character of the artist's signature is fully preserved. After this process, the designs are printed onto specially prepared paper spread with a layer of glue. This makes it easier to lift the colour decorations off the paper and onto the porcelain. The colours are applied onto the paper using the screen-printing method. Very finely meshed metal screens allow the colour to permeate only in desired areas. Each colour is printed separately, which means that a new screen has to be prepared each time. The different colours are printed one after the other and aligned exactly. Screen-printing allows a strong application of colour, which after firing produces a rich glow of colour. After printing, the transfer sheet is coated with a layer of lacquer. In order to decorate a porcelain piece, the decal is soaked in water to dissolve the layer of glue. The flimsy and wet colour film is then carefully applied to the porcelain.

Decorative transfers

The most frequently used technique for decorating porcelain is to apply a sheer, wet colour film. This process demands extreme precision, patience, a steady hand and a sharp eye. These days, decorative transfers are no longer used to decorate tableware alone, they are also applied to valuable limited porcelain editions, which cannot be painted by hand without altering the original design of the artist.

Hand painting

Lustre, gold and platinum bands, handles, spouts and gilded reliefs are all hand painted. after firing, fibreglass brushes are used to burnish the gold layer to a high gloss.


Photo: The iconic head of Medusa adorning the Rosenthal meets Versace collections is gilded by hand and looks brown in its unfired state.

Base colouring

When larger areas of a porcelain piece are to be coloured, the colour foundation is distributed evenly with a spray gun. All areas that are to remain white are varnished beforehand with a lacquer that must be removed after spraying. After removal of the lacquer layer and before firing, the white areas of the porcelain are cleaned carefully. Even the tiniest amounts of colour residue would turn into visible spots after firing.


Photo: Ensuring that the colour is applied evenly by hand requires a great deal of experience.

Combination matt – glossy

There are several methods to produce the combination matt – glossy.

  1. Matt glaze is sprayed onto the porcelain in a similar fashion to a colour base using a spray gun and then fired.
  2. Glazed porcelain can be made matt by sandblasting.
  3. The areas that are to remain matt and unglazed are covered with wax before being dipped into the glaze. The wax burns off during sharp firing.

Decoration firing

High temperature decoration firing

High temperature decorations are either transfer-printed, hand painted or sprayed onto the finished porcelain. With in glaze decoration firing, in contrast to under glaze firing, considerably more shades of colour as well as gold and platinum can be melted into the glaze. In only 90 minutes, the porcelain is heated to 1230 ̊ C so that the decoration sinks into the liquefied glaze, which protects it at the same time. Gold decorations are also polished to a high gloss after decoration firing using fibreglass brushes. High temperature decorations remain unaffected by outside influences and are dishwasher safe.


On glaze decoration firing

On glaze decorations are also applied to the finished porcelain using transfers, spraying techniques or hand painting and are fired at temperatures of around 850 to 950 ̊ C.

Care tips

Although porcelain is an exquisite material, it has great design versatility and can be used for a variety of applications. White porcelain with no decorations is always suitable for cleaning in the dishwasher. Porcelain with decorations is only dishwasher safe if the decoration is melted into the glaze (in glaze/under glaze), where the glaze absorbs the decoration. Its colours and luminescence then become indestructible as well as scratch- and rub-resistant.

To ensure that you continue to enjoy your porcelain over the long term, we recommend the following care tips:

-Check whether your porcelain is dishwasher suitable.

-Read the recommendations of your dishwasher manufacturer on handling, cleaning and maintaining your appliance.

-Stack items in the dishwasher in such a way that the porcelain does not touch or rub against other items during the cleaning cycle.

-Always clean black porcelain by hand.


.Dishwasher safe

The product can be placed into the dishwasher without reservation.


.Dishwasher suitable

The colours of this pattern are fired onto the glaze at (at least) 840° C. The resistant colours used achieve a strong bond with the glaze. The product can be cleaned in the dishwasher using the delicates cycle at a temperature of 55°C. Do pay attention to the guidelines of dishwasher and detergent manufacturers on the suitability of their products.


.Precious decoration

This product must always be cleaned by hand. Use of precious colours and artistic decorations means that the item cannot be cleaned in the dishwasher.


.Microwave suitable

The product can be placed into the microwave without reservation.

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