Lead Oxide - PbO

Metal Flux Unit 6 Topic 8
Oxide Qualities

Strong low to mid range flux - low expansion - oxidation only.
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Action

  • Is a very active flux combining with other oxides very easily.
  • Gives a high brilliance and has a low coefficient of expansion.
  • Increases the stretching ability of the glaze and decreases the viscosity.
  • Can be used from C.015 to C.O2 (some say C.6). Long firing range avoids under or over firing.
  • The only oxide that can stand alone in the flux group of a unity formula.
  • Not suitable for temperatures over 1100 deg.C due to volatility of the oxide.
  • Lead glazes tend to be soft and easily scratched.
  • Very easily reduced producing detrimental grey discolouration and blistering.

Soluble Sources

  • White lead (litharge) PbO, red lead Pb3O4 and lead carbonate (cerussite) PbCO3 are no longer available or used in raw glazes. They are used instead to produce lead bearing fritts.

Insoluble Sources

  • Lead orthosilicate 2PbO.SiO2. Good for low temperature glazes (melting point 700 deg.C)
  • Lead monosilicate PbO.SiO2. (melting point 800 deg.C).
  • Lead bisilicate PbO.2SiO2. (melting point 900 deg.C).
  • Lead sesquisilicate 2PbO.3SiO2. (melting point 850 deg.C).

Colour Responses

  • High lead glazes can give a yellowish colour.

Raw lead metal and its soluble compounds are highly toxic and can be released from low durability glazes under certain conditions.

Copper should not be used as a colourant in or on lead bearing glazes as it promotes the leaching of the lead content of the glaze.

If lead is to be used in glazes it should be introduced in a fritted (insoluble) form and then only in carefully balanced glazes.

The use of lead fritts reduces the danger of handling this lead bearing material but does not reduce the risk of lead eventually being released from a fired glaze.
Check the health data on lead oxide - red lead

http://www.jtbaker.com/msds/l3391.htm
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