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All colours of Greek black-red vase painting are produced by the different concentrations of iron in the clay, and the different degrees to which that iron is oxidised during firing. Iron has the special feature of forming oxides of various colours, including grey Iron(II) oxide (FeO), red Iron(III) oxide (Fe 2 O 3), and deep black magnetite ...
A series of analytical studies have shown that the striking black gloss with a metallic sheen, so characteristic of Greek pottery, emerged from the colloidal fraction of an illitic clay with very low calcium oxide content. This clay slip was rich in iron oxides and hydroxides, differentiating from that used for the body of the vase in terms of ...
Raw materials for ceramic glazes generally include silica, which will be the main glass former. Various metal oxides, such as those of sodium, potassium and calcium, act as flux and therefore lower the melting temperature. Alumina, often derived from clay, stiffens the molten glaze to prevent it from running off the piece. [7]
The iron in the clay absorbs oxygen and becomes the red or red-brown iron(III) oxide. The resulting pottery has a red-brown colour. [25] The simplest and earliest firing method is the open fire. The vessel to be fired is covered and filled with flammable material. It is placed on a flat piece of ground, surrounded by a low wall, or put in a pit.
Maiolica charger from Faenza, after which faience is named, c. 1555; diameter 43 cm, tin-glazed earthenware Tin-glazed (majolica/maiolica) plate from Faenza, Italy. Tin-glazed pottery is earthenware covered in lead glaze with added tin oxide [1] which is white, shiny and opaque (see tin-glazing for the chemistry); usually this provides a background for brightly painted decoration.
Sodium from the salt reacts with silica in the clay body to form a glassy coating of sodium silicate. The glaze may be colourless or may be coloured various shades of brown (from iron oxide), blue (from cobalt oxide), or purple (from manganese oxide). [1] [2] [3] Except for its use by a few studio potters, the process is obsolete. Before its ...
Unglazed terracotta is suitable for use below ground to carry pressurized water (an archaic use), for garden pots and irrigation or building decoration in many environments, and for oil containers, oil lamps, or ovens. Most other uses require the material to be glazed, such as tableware, sanitary piping, or building decorations built for ...
Red ochre – natural minerals containing silica and clay some of which is composed of iron oxide and hematite (anhydrous iron(III)-oxide) Yellow ochre – natural minerals that contain silica and clay, and attributing to its color, goethite (iron oxyhydroxide) Lime white – chalk (calcium carbonate and calcite)