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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 ...
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.
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.
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 ...
Underglaze transfers are a technique that involves screenprinting or free handing a pattern onto a transfer paper (often rice paper or newspaper) which is then placed, dampened, and burnished onto the surface of a leather-hard piece of clay (similar to how a lick-and-stick tattoo might be applied). [21]
At the same time in China, green-glazed pottery dating back to the Han period (25–220 AD) gave rise eventually to the sancai ('three-color') Tang dynasty ceramics, where the white clay body was coated with coloured glazes and fired at a temperature of 800 degrees C. Lead oxide was the principal flux in the 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 ...