After almost 200 years the magistral formula, which in its correct proportions produces the characteristic fine pottery of La Cartuja de Seville, maintains the same ingredients: quartz, kaolin, feldspar, silica, clay and others.
The mixture of which results in a dark mass called ‘barbotine’ that can appear in two forms: liquid, for the elaboration of hollow pieces such as soup terrines, jugs, etc., and solid for flat shapes such as plates and serving dishes, etc.
Moulding can vary depending on the piece. In the case of flat pieces, the process is simpler. This was something that used to be done by hand by extending the solid mix over a mould. Today, it is very similar but this is now done by a specialised machine.
When we are dealing with hollow pieces, the process is more elaborate and it is done in the same as it has always been done. The barbotine , or slip is poured inside the plaster mould. There is a mould for each piece. Once the mix has set along its walls and appears to be thick enough, the excess material is removed and the mould is detached so that the drying process can begin.
After a suitable consistency has been reached, the piece is tidied up manually with a knife to remove any excess and unwanted clay. Finally, the piece is finished thanks to the artistry carried out with a humid sponge.
Each piece will go through three firings. During the first, the piece will remain in the kiln at a maximum temperature of 1,150 degrees centigrade for sixteen hours until the biscuit is hard and white.
Classification of the biscuit and stamp
In the following step the first important screening is carried out, and only those pieces that meet the highest quality standards are selected to carry on to the next stage. Next, they will be given La Cartuja de Sevilla stamp; this process is authentic as we still stamp each piece at the factory with artisanal serigraphy, direct applied by hand.
Historically four main decoration techniques have been used: stamping, cloisonné, hand painting and transfers.
The most commonly used is the underglaze transfer. The first transfers were introduced in 1910 and came from England, France and Germany. The technique, unchanged since its origins, consists in decorating pieces with patterned paper that had previously been printed via a photolithographic process. The paper is applied manually by our decorators on the pieces in their biscuit stage of elaboration, after the first firing and after applying a sealer. The sealer is a plastic liquid applied and facilitates the process.
This is the second firing and its aim is to fix the colours. It is carried out at 800 degrees centigrade asn takes 8 hours.
The glaze involves submerging the piece in varnish, by hand and piece by piece. After this, the third firing takes place at 1,020 degrees centigrade, which gives brightness and transparency and also strengthens and protects the colours in the decoration.
Classification and finishing off
This is the final stage which completes the complex artisanal process for each and every one of the pieces at La Cartuja de Sevilla.
These eight steps summarise the full process, which entails eighteen different one in total, eight of which for quality control.