Glazed ceramic. It is a ceramic that is obtained when the terracotta (base of all ceramics) is vitrified, that is, it is covered with an enamel produced from a varnish based on lead or other substances, also called fried or marzacotto. The term glazed is used to designate in a general way the glass film that covers the ceramic products.
Although some sources attribute its invention to the China of the third century BC . C., and its arrival in the West to ancient Rome , there are earlier testimonies in the Ancient Near East, such as the Egyptian faience (Naqada Culture 3500 – 3200 BC), or the ceramics of Babylon (Ishtar Gate, century VI a. C.). The use of glazed ceramics to beautify the walls was used in Islamic art since the Middle Ages , giving rise to tiles.
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- 1 Manufacturing techniques
- 2 types of ceramics
- 1 Glazed ceramics in Lorca
- 3 Realization process
- 4 Sources
With the presence of Islamic culture in the Iberian Peninsula, the use of glazing was generalized due to its prophylactic effects (it waterproofs and prolongs its life by preventing it from rotting by absorbing its contents). As in the other decorative techniques, the glaze had been used since at least the second millennium BC, but it will be during the Middle Ages when glazed ceramics reach a great development, especially those related to cooking and tableware.
The glaze was obtained by applying a monochrome vitreous varnish just before cooking. The pieces were submerged in a mixture composed of two products; a flux and other dye, whose composition varied depending on the color one would like to obtain (green, manganese oxide, molasses, copper oxide).
The glaze appears in numerous types of ceramics in the Middle Ages . It is found in kitchen ceramics (casserole, pot), mainly on its inner face and on the edge, covering the areas that will be in direct contact with food. It is also documented in fire containers (lamps), and in tableware, which appear glazed on its entire surface if they are open forms (bowls, attackers) or only outside if they are closed forms (bottle, redoma).
As in other decorative techniques, it is common to document the combination of two of them; manganese and sgraffito, glazed and stamped or, glazed (colored in color) on lines painted in manganese. This was achieved by drawing dark lines on the surface of the piece, on which the vitreous varnish was applied. Another technique was the so-called blue on white that was achieved by applying a tin oxide on the ceramic surface that achieved a white cover on which the colors in blue were applied.
Glazed pottery in Lorca
The oldest Andalusian glazed ceramics found in Lorca are from the 9th century and come from silos of the Glorieta de San Vicente and from a house excavated on Eugenio Úbeda street. There is evidence that the potters of Lorca made glazed ceramics, as documented in a thirteenth-century kiln excavated in Empedrada Street, whose last production was made of jofainas and green glazed coffin.
The terracotta object is covered with lead oxide powder and placed in the oven at a temperature of 750 centigrade. As terracotta clay contains silica, when it comes into contact with lead oxide it merges and a transparent glass film appears on the entire surface. If this fusion is also amalgamated with other oxides, the result may be colored:
- Yellowor brown with iron oxide
- Green, with copper oxide
- Blue, with cobalt oxide
- Purple, with manganese oxide
In the Middle Ages they also used another system: they mixed a type of silica-based clay with wine waste ; then they finely ground the mixture and added lead oxide . The resulting mass served to cover the terracotta and give it the finish.