The first raw material used by the Homo sapiens was the barro. With it he built utensils, their houses and the first artistic forms, either to create anthropomorphic figures or to model zoomorphic figures. The next step was to decorate his creations with different color nuances.
The birth of the ceramics It dates back to the Neolithic period -around 10,000 BC-, which was when the first containers for storing food and water appeared.
Etymologically the word ceramic comes from the Greek ‘ceramic‘, feminine form of’ceramicist‘, What does it mean ‘burned substance‘. With this term the potters’ quarter of ancient Athens was designated, the artisans in charge of making objects from fired clay.
Metal oxides and decoration
The ceramic industry, from a chemical point of view, is based on the binary combinations between oxygen and metallic elements, such as copper, manganese or lead. The properties of materials are dictated by the types of atoms present and by the bond that is established between them. Generally they usually have a combination of ionic bonds, between a metal and a nonmetal, and covalent bonds, between the nonmetallic elements. They are responsible for the hardness, the high melting point, the low thermal expansion and the excellent chemical resistance.
The metal oxides that participate in the composition of ceramics can be grouped into three categories: fluxes, opacifiers and colorants. The first ones are those that allow to lower the melting point of the mixture and get all the components to melt during cooking. There are basically two types, those that act as fluxes at low temperatures (lead, lithium, potassium and sodium) and those that do so at high temperatures (calcium, barium, magnesium and strontium).
The next group would be formed by the metallic oxides that serve to opacify, that is, to eliminate the natural transparency of the glazes and obtain opaque covers. In this group we find zinc, titanium, tin and zirconium oxides.
Last but not least, there would be the metallic oxides that provide color and are those that are present in the oldest ceramics, since they were the first to be used to decorate the surface of the vessels. Among them are iron oxide, which generates reddish and brown tones; copper oxide, responsible for greens and turquoise; cobalt oxide, for bluish tones, or manganese oxide, when what you want to achieve are earthy or violet colors.
The use of manganese, copper and tin oxide was the decorative base of the famous Caliphate ceramics, and it was with these chemical substances that their well-known green colors (manganese oxide) were achieved on a whitish base (dioxide tin). The manganese green of Caliphate ceramics, coming from the Medina Azahara workshops, managed to impose itself on the tastes of the time.
In al-Andalus the sgraffito technique was also developed, which consisted of covering ceramic objects, mostly small jugs, with a layer of manganese oxide, which was ‘scratched’ with a burin to form the different decorative motifs (vegetal, symbolic, zoomorphic, figurative, geometric or epigraphic forms).
It was also the oxides, specifically those of cobalt, tin and copper, which gave Nasrid ceramics their famous blue and green tones on white backgrounds. A ceramic with metallic reflections whose origins must be sought in Egypt and Syria.
Pedro Gargantilla is an internist at the Hospital de El Escorial (Madrid) and the author of several popular books.