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Minton majolica game pie dish, lead-glazed earthenware, c. 1875, an iconic example of High Victorian appetite for innovation with humour/whimsy, coloured lead glazes. Lead-glazed earthenware is one of the traditional types of earthenware with a ceramic glaze, which coats the ceramic bisque body and renders it impervious to liquids, as ...
A ceramic flux functions by promoting partial or complete liquefaction. [1] [2] The most commonly used fluxing oxides in a ceramic glaze contain lead, sodium, potassium, lithium, calcium, magnesium, barium, zinc, strontium, and manganese. These are introduced to the raw glaze as compounds, for example lead as lead oxide.
A high-lead glaze has a linear expansion coefficient of between 5 and 7×10 −6 /°C, compared to 9 to 10×10 −6 /°C for alkali glazes. Those of earthenware ceramics vary between 3 and 5×10 −6 /°C for non-calcareous bodies and 5 to 7×10 −6 /°C for calcareous clays, or those containing 15–25% CaO. [16] Therefore, the thermal ...
Ceramic industries are reluctant to use lead alternatives since leaded glazes provide products with a brilliant shine and smooth surface. The United States Environmental Protection Agency has experimented with a dual glaze, barium alternative to lead, but they were unsuccessful in achieving the same optical effect as leaded glazes.
Galena is the primary ore of lead, and is often mined for its silver content. [6] It is used as a source of lead in ceramic glaze. [27] Galena is a semiconductor with a small band gap of about 0.4 eV, which found use in early wireless communication systems.
A parting and contraction of the glaze on the surface of ceramic ware during drying or firing, resulting in unglazed areas bordered by coalesced glaze. May be caused by uneven glazing, excessive glaze thickness or a greasy substrate. [8] Crazing A glaze fault characterised by the cracking of fired glazes and due to high tensile stresses.
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Sancai is a type of lead-glazed earthenware: lead oxide was the principal flux in the glaze, often mixed with quartz in the proportion of 3:1. [6] The polychrome effect was obtained by using as colouring agents copper (which turns green), iron (which turns brownish yellow), and less often manganese and cobalt (which turns blue).
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