To prepare the clay body,50% white clay (kaolin) is mixed in large vats with 25% feldspar and 25% quartz – all finely powdered – and dissolved in water.
The porcelain body is then further refined according to the shaping technique that will be used. The liquid mass (slip) for mold casting can be used after just two days of processing, while the firmer sculpting mass, for use on the wheel, needs to be stored at least a few weeks in the “aging room” before it can be further processed.
THE WORKSHOPS AT HÖCHST PORCELAIN MANUFACTORY
Today, the “white gold” of Höchst is created in the new “Porzellanhof” building next to the city park in Höchst. Here visitors can experience the fascination of porcelain manufacturing in person, and can learn about the entire process of crafting pieces at Höchst Porcelain Manufactory during public and private tours.
The Porzellanhof was built in 1906. The impressive industrial building is historically protected and now houses all of the workshops used for manufacturing Höchst porcelain.
Clay body preparation
Model workshop
This is the heart of the Manufactory! Here our creative workers design the models, from initial sketches to large-scale production drawings, from sculptural models out of plaster or clay to the final model – the tool used for manufacturing the molds later.
Mold manufacturing
Since every molded piece requires a multi-piece plaster model, the equipment blocks are used to cast the individual model elements.
Each model is replaced after it has been used to produce twenty to thirty molded pieces, and the casting process then starts from the beginning.
Casting
The rotary casting machine is used for casting hollow shapes, such as vases, pitchers and parts of figurines. Fall pipes are used to transport the porcelain slip from storage vats to the workstations. The plaster molds are filled with the slip. The plaster draws the water out of the body; the longer the slip stays in the mold, the thicker the layer of porcelain that forms on the inside wall of the plaster mold.
After a certain waiting period, the excess slip is poured out into storage vats. After the drying period – which varies according to the piece – the plaster molds can be opened, and the castings are carefully removed.
Jiggering
In addition to manufacturing mugs and cups, jiggering technology is mainly used for manufacturing flat pieces such as platters, plates and saucers. In this process, sections of clay body are cut into disks and shaped by jiggering the plate shape with a metal molding tool as they rotate on the wheel; when shaping cups, the plaster form is inserted into the rotating clay body.
Embossing
The delicate cast pieces, often many individual components of one figure, must be carefully smoothed while they are still damp and leather-hard, and then skillfully assembled using porcelain slip. This process is known as embossing; the term comes from the French word “bosseler” (German: “bosseln”), as does the profession of embosser.
Glazing
After the drying process and bisque firing at 920°C, the pieces are glazed. First our logo, the Mainz wheel with the name HÖCHST, is stamped onto the still-porous body in a blue underglaze (cobalt blue).
Next the piece is dipped into a glaze bath. The glaze is a milky liquid; like the porcelain body, it is made up of kaolin, quartz and feldspar, but with a higher proportion of flux materials and water.
Firing
The actual porcelain firing, or glaze firing, takes place at 1390°C in a gas-fired kiln. In the process, the raw material is sintered, becoming completely solid, and the glaze is permanently fused onto the clay body.
Porcelain painting
The high-quality craftsmanship and aesthetic of Höchst porcelain depends in large part on the traditional hand painting that is still performed in the manufactory today. Whether for traditional Höchst designs or modern design pieces, the artists of Höchst Porcelain Manufactory are masters of their work. Contract work, such as producing limited special editions (artists’ series), is just one of the challenges that our talented porcelain painters handle on a regular basis.
