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Major Oxides / 主要陶瓷氧化物

Chemical composition and molecular weights, for use in glaze formula calculations.

MATERIALS

COMPOSITION

MOL. WT.

Alumina, Aluminum Oxide 氧化鋁

Al2O3

101.94

Alumina hydrate 氫氧化鋁

Al2(OH)6

156

Barium carbonate 碳酸鋇

BaCO3

197

Borax 硼砂

Na2O2B2O310H2O3

382

Boric acid (boracic acid) 硼酸

B2O33H2O

124

Calcined clay 鍛燒高嶺

Al2O32SiO2

222

China clay (kaolin) 高嶺土

Al2O32SiO22H2O

258

Colemanite 硬硼鈣石

2CaO3B2O35H2O

412

Cornwall stone 康瓦爾陶石

Dolomite 白雲石

CaCO3MgCO3

184

Flint (silica) 燧石、石英

SiO2

60

Fluorspar, fluorite 螢石

CaF2

78

Lead bisilicate 矽酸鉛

PbO2SiO2

343

Lead carbonate (white lead) 碳酸鉛

2PbCO3Pb(OH)2

775

Lead monoxide (litharge) 黃色氧化鉛 、黃丹

PbO

223

Lead oxide (red lead) 紅色氧化鉛、紅丹

Pb3O4

685

Lithium carbonate 碳酸鋰

Li2CO3

74

Magnesium

MgCO3

84

Nepheline syenite 霞石正長石

Niter (potassium nitrate) 硝酸鉀、硝石

KNO3

101

Peal ash (potassium carbonate) 碳酸鉀

K2CO3

138

Soda ash 碳酸鈉

Na2CO3

106

Talc (steatite) 滑石

3MgO4SiO2H2O

378

Tin oxide 氧化錫

SnO2

151

Titanium oxide (rutile) 氧化鈦、金紅石

TiO2

80

Whiting (calcium carbonate) 碳酸鈣

CaCO3

100

Wallastonite 矽灰石

CaSiO2

116

Zinc oxide 氧化鋅

ZnO

81

Zirconium oxide 氧化鋯

ZrO2

123

Zircopax (zirconium silicate) 矽酸鋯

ZrO2SiO2

183

  • SiO2 - Silicon dioxide - 二氧化矽 - 二氧化硅
    • Supplied by flint, feldspar, and kaolin. It is the principle glass forming oxide and normally comprises more than 60% of most glazes and clays. It has a low expansion and high melting temperature.
    • Increase it at the expense of B2O3 to make glaze harder, more durable, and brilliant. Boric oxide and silica can be interchanged to vary a glazes temperature.
    • Decreasing SiO2 increases the melt fluidity; increasing it raises the melting temperature, increases acid resistance, lowers expansion, increases hardness and gloss, and increases devitrification.
    • It is normal to use as much as possible in any glaze to keep expansion low, to prevent crazing, and enhance body/glaze fired strength. Note, however, that in certain boracic and feldspathic compositions it can increase crazing so that other low expansion oxides may be needed to reduce glaze expansion.
    • With boron and alumina, it has the lowest expansion of all oxides.
  • Al2O3 - Aluminum oxide - Alumina - 氧化鋁 - 明礬
    • Supplied by kaolin and feldspar. It combines well with silica and basic oxides to give body, durability, and stability to glazes. It has a low expansion and high melting temperature.
    • Alumina controls the flow of the glaze melt, preventing it from running off the ware. It is thus called an intermediate oxide because it helps build strong chemical links between fluxes and silica.
    • In most cases, the addition of alumina raises the melting temperature of a glaze or glass. However, in some soda lime formulations, a small alumina addition can decrease melting temperature.
    • Alumina (preferably in the calcined form) can be used in clay bodies as an aggregate and filler in place of flint. This can increase the firing range, decrease quartz inversion firing problems, and increase hardness and whiteness in the fired body. However, alumina is much more expensive than flint.
    • Alumina hydrate promotes opacity in enamels and glazes by generating gas bubbles in the glaze melt.
  • B2O3 - Boric oxide - 氧化硼
    • Supplied by borax frits, gerstley borate/ colemanite. It is a low temperature low expansion equivalent of silica.
    • Boron glazes are less fluid and this has been the major challenge in switching from lead. While many users have increased firing temperatures to compensate, this has not fully solved the 'healing' and bubble clearance problems.
    • In low temperature glazes, it both substitutes for fluxes of high-expansion, and for silica which cannot be present in large amounts.
    • The action of B2O3 depends upon the ratio of bases to silica existing in the glaze before the addition. If the ratio is greater than 1:2, the glaze will tend toward opalescence and crazing; if less toward clear and transparent.
  • CaO - Calcium oxide - Calcia - 氧化鈣 - 生石灰
    • Supplied by whiting, wollastonite, feldspar, colemanite, dolomite or quicklime. It is the principle flux in medium and high fire glazes. In higher amounts it can give matte qualities through the formation of calcium silicate crystals.
    • Quicklime is pure calcia, but it reacts with water to produce calcium hydroxide or slaked lime. Calcium oxide, on the other hand, is an extremely stable compound.
    • Calcium oxide is the principle flux in medium and high temperature glazes, beginning its action around 1100C. It must be used with care in high-fire bodies because its active fluxing action can produce a body that is too volatile (melting if slightly overfired).
    • Calcia usually hardens a glaze and makes it more scratch and acid resistant. This is especially so in alkaline and lead glazes. Its expansion is intermediate.
    • CaO is not effective below cone 4 as a flux in glazes but in small amounts (less than 10%) it can dissolve in earthenware glaze melts especially with lead, soda, potash) to add hardness and resistance to leaching. In non-lead mixes it can also help reduce crazing. In larger amounts, it encourages the growth of crystals which can give decorative effects to glossy glazes and produce matteness (i.e. 30%).
    • Calcia is a moderate flux in the cone 5-6 range, but a very active one at cone 10.
    • High calcia glazes tend to have good (although sometimes unexpected) color responses. For example, in oxidation iron glazes calcia likes to form yellow crystalline compounds with the Fe2O3 producing a 'lime matte'. Without the calcia, glossy brown glazes are the norm.
      The term 'lime' encompasses several different minerals and manufactured products.
      The term 'Whiting' traditionally refers to calcium carbonate produced by the grinding of chalk from the cliffs of England, Belgium and France. However this title also refers to any ground calcium carbonate material (i.e. those processed from marble and calcite ores).
      Dolomite (magnesium carbonate) is a mineral which supplies some magnesia in addition to its CaO complement. It is preferred in many situations because it more readily fluxes and the magnesia imparts desirable properties.
      Wollastonite is a calcium silicate which is more expensive than other sources of calcium, but is used bodies, glaze, porcelains, enamels and frits for its many superior properties.
  • K2O - Potassium oxide - 氧化鉀
    • Supplied by potash feldspar and cornwall stone. It is an important auxiliary flux in high temperature glazes. It has a high expansion.
    • K2O is considered together with sodium, since the two almost always occur together and have very similar properties. When taken together the two are often labeled KNaOK2O generally promotes higher melt viscosity than Na2O.
    • It is an important auxiliary flux in high temperature glazes.
    • It is a heavy oxide and in general hosts the brightest colors of all fluxes except for lead.
  • Na2O - Sodium oxide - Soda - 氧化鈉 
    • Supplied by feldspar, nepheline syenite and sodium frits. A slightly more powerful flux than potassium for high temperature glazes. It has a high expansion.
    • Soda is a slightly more powerful flux than potassium. Together with potassium and lithium oxides, it is classified as one of the Alkaline group.
    • Sodium is a useful flux over the entire temperature range from 900ºC-1300ºC. It is very active at higher temperature ranges.
    • Soda should be used in moderate amounts because it has a higher expansion than any other oxide and will promote crazing in glazes lacking silica or alumina. Also it decreases tensile strength and elasticity compared to other common bases. High soda glazes can often be soluble and easily scratched.
    • Soda works well with boric oxide (and also Lithia and potassium) in low temperature lead-free glazes.
  • MgO - Magnesium oxide - Magnesia - 氧化鎂
    • Supplied by talc or dolomite. At lower temperatures, it is a matting agent and opacifier; at higher temperatures, it is an active alkaline flux.
  • Fe2O3 -三氧化二鐵, Fe3O4 - 四氧化三鐵- FeO-Ferric oxide -氧化鐵,
    • Supplied by iron oxide and stained clays. It is the most popular colorant. In a reducing atmosphere, it can act as a flux in both bodies and glazes at high temperatures.
  • ZnO - Zinc oxide - 氧化鋅
    • Available in a pure state. It is a low expansion secondary flux, in moderate to higher amounts it acts to produce mattes and crystalline surfaces.
  • TiO2 - Titanium dioxide - 二氧化鈦
    • Available pure or in rutile. It is a complex material because of its opacifying, crystallizing, and multitude of color responses.
  • ZrO2 - Zirconium oxide - 氧化鋯
    • Available in a pure state and is supplied by zircon opacifiers. It is used to opacity glazes. Zirconium has a very low thermal expansion.
  • BaO - Barium oxide - 氧化鋇
    • Supplied by barium carbonate. It is a flux which encourages the growth of micro-crystals to produce attractive satin-matte surfaces. It also has unique color responses.
  • Li2O - Lithium oxide - 氧化鋰
    • Supplied by lithium carbonate or lithium feldspar (i.e. spodumene - 鋰輝石). It is a powerful auxiliary alkaline flux. Its expansion is lower than soda or potash.
  • PbO - Lead oxide - 一氧化鉛 - 密陀僧
    • Supplied by lead frits. It reacts easily with silica to form low melting lead silicates of high gloss and deep character.
  • SrO - Strontium oxide - 氧化鍶
    • Supplied by strontium carbonate. It has matting and crystallizing properties similar to barium although it produces brighter and more fusible glazes with fewer surface defects.