Pottery and China An Introduction

Pottery One of the oldest (evidence exists back to 10,000 B.C.) forms of fabricating utilitarian objects from natural resources (clay). Cooking and eating objects, containers, decoration. Mechanical aspects: crush, grind, and mix clay; add water; shape object, fire pottery with or without glaze.

Industrial Revolution Chemistry is involved in setting the clay mixture – type and amounts, making the glazes, and selecting the correct clay + glaze combination. Like textiles, the pottery industry became mechanized and grew rapidly for many of the same reasons that the textile industry did. New inventions, advances in power, new markets and sources of raw materials, improvements in transportation.

Earthenware, Stoneware, Porcelain These contain naturally occurring clays or minerals resulting from the chemical weathering of rocks (e.g. + acid). Identity of the minerals (mostly silicates = Si + O) and proportions vary. Some examples – (A)Antigorite: Mg 3 Si 2 O 5 (OH) 4 – (K)Kaolinite: Al 2 Si 2 O 5 (OH) 4 – (Q)Quartz: SiO 2 – (F)Potassium Feldspar: KAlSi 3 O 8

A Look at the Minerals Kaolinite: kaolinit/kaolinit.htm kaolinit/kaolinit.htm Quartz: artz/quartz.htm artz/quartz.htm Feldspar: microcli/microcli.htm microcli/microcli.htm

From Minerals to Pottery, China Clay + water is plastic and can be shaped into objects. Heating or firing the resulting pot or dish at high temperatures expels the water and produces physical and chemical changes. As the firing temperature increases, the clays become more vitreous (like glass, amorphous), less porous and harder, more translucent.

How Pottery Types Differ Kiln or Firing Temperature – Earthenware : o C – Stoneware: o C – Porcelain: o C Composition – Earthenware: A:K:Q:F = 25%:28%:32%:15% – Porcelain has mostly K Earthenware: most porous, opaque, coarse

Glaze Glazes serve several functions: make an object less porous, make it stronger and for decoration. Glazes are vitreous or glassy materials that have various colors, consistencies. They are applied to the kiln-fired object and then fired again to make the glaze adhere to the object.

Composition of Glazes Silica is the main component of glaze: SiO 2 Flux to help melt the glaze: e.g. BaO, CaO, Na 2 O, PbO Stabilizer to extend glaze MP and stiffen glaze: alumina, Al 2 O 3 Opacifier to make glaze opaque: e.g. SnO 2, TiO 2 Colorant: metal oxides

Glazes Impart Color Metal oxides, inorganic compounds Metal atoms absorb light and emit visible light; recall the discussion about textile dyes. CuO, CuCO 3, CoO, CoCO 3, MnO 2, Fe2O 3, TiO 2, V 2 O 5, NiO

References