MANUFACTURE NATIONALE DE SÈVRES

The making of a Sèvres porcelain plate
 
The plaster mould
 
Apart from throwing, the various methods of plate manufacture involve the use of plaster moulds taken from plaster models. The models for Duplessis and Pimprenelle-type plates are produced in the sculpture and modelling workshop based on a technical drawing; the lobed rims and reliefs are cut directly on the model. The models for Uni and Diane-type plates are produced in the moulding and plaster-throwing workshop based on a plaster line-drawing.
 
The latter workshop is also responsible for making the plaster moulds used at the Manufacture de Sèvres. Two consecutive imprints are required to obtain the mould to be used for the reproduction of a porcelain plate. The first imprint of the model is concave and known as the first mould; the second, called a jack, is taken from the first mould: it is convex and an exact replica of the model.
 

Jiggering
 
In the 18th century, porcelain plates were moulded. The technique of jiggering was adopted at the Sèvres Factory in the 19th century and systematically applied from 1842 onwards. The French term calibrage derives from the metallic template (calibre) used in the final stage of the production process, a process carried out on three rotating posts. On the first post, which is fitted out with a flat surface called a basane, the jiggerer centres and kneads a ball of paste, which he then flattens out evenly with a steel knife. This layer of paste is known as the croûte.
 

 

 

 
The basane and its layer of paste are turned upside down and placed over the mould on the second working post. The jiggerer then detaches the paste with a box-wood knife manufactured on site and, working evenly and exactly, presses it down on the rotating mould with moistened organic sponges known as elephant ears to fashion the inner side of the plate. For moulds with deep reliefs, the imprint is produced on a static mould by applying a fixed pattern of regular taps with a special hammer (mailloche). The reliefs cannot be touched up afterwards.

The plate, still stuck to its mould, is then transferred to the third working post. The latter is fitted out with a steel template made on site to match the paste line-drawing of the plate’s contours when not yet dried (greenware). The thickness of the plate and its outer profile are obtained by manually lowering the template onto the rotating paste. Following two different and consecutive dryings, the plate in dry unfired paste is reworked on the wheel using an implement made of dry paste known as a chuck. The surface is polished (déglacée) with an abrasive and with tow, and each linear rim is formed on the jigger, whereas lobed rims are cut and polished manually, one by one, by the découpeuses-garnisseuses (craftswomen in charge of cutting and ornamenting). It is at this stage that the first workshop hallmarks are affixed.
 
After shaping, the plates are fired at 980°C in a kiln known as a dégourdi. This temperature, somewhat low for porcelain, preserves their porosity, a prerequisite for glazing.
 

Glazing
 
In the dip-glazing workshop, a workshop hallmark and the manufacturer’s mark are affixed to the plates, which are then dusted.
 
The mark Sèvres has been using since 1970 was designed by Georges Mathieu.
 
The transparent colourless glaze is made of pegmatite and quartz and is produced on location. A thin layer is applied by rapidly dipping each plate in a glaze bath containing the raw materials in an aqueous suspension. The composition of the glaze bath varies according to the porcelain paste; its density is decided in the workshop (1.365 kg/l. for plates). Furthermore, the glazer has to hold each type of product in a different manner: plates are held by three fingers on the footring.
 


 
After air-drying for 48 hours, the plate is touched up on a rotating plaster chuck in three stages: 1) to remove drips, finger smudges and flaws known as dentelles; 2) to even out the surface; and 3) to remove the glaze from the footring. After glazing and firing in kilns known as kilns for whites, generally at 1,380°C in a reducing atmosphere, the footrings are polished in the polishing workshop.
 
The sorting workshop selects the fired plates before decoration, at which point several marks are affixed.