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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 ...
In the classical process to make lustreware, a preparation of metal salts of copper or silver, mixed with vinegar, ochre, and clay is applied on the surface of a piece that has already been fired and glazed. [7] The pot is then fired again in a kiln with a reducing atmosphere, at about 600 °C. The salts are reduced to metals and coalesce into ...
Alumina, often derived from clay, stiffens the molten glaze to prevent it from running off the piece. [7] Colorants, such as iron oxide, copper carbonate or cobalt carbonate, [7] and sometimes opacifiers including tin oxide and zirconium oxide, are used to modify the visual appearance of the fired glaze.
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 [1] [2] [3] Except for its use by a few studio potters, the process is obsolete.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 ...
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.
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.
Common red clay and shale clay have vegetable and ferric oxide impurities which make them useful for bricks, but are generally unsatisfactory for pottery except under special conditions of a particular deposit. [18] Bentonite: An extremely plastic clay which can be added in small quantities to short clay to increase the plasticity.