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Medium Temperature or Mid-Fire Glaze


In functional ceramics this term generally refers to glazes that mature from cone 4 to 7. At these temperatures it is difficult to compound glazes that will melt well without the need for powerful melters like zinc and boron. Thus a medium temperature glaze contains mostly the same kinds of ingredients as a high temperature one, but additionally it needs a source of zinc or boron (boron is by far more popular and less troublesome). Typically frits are employed to supply the B2O3. Historically Gerstley Borate and Colemanite were very common sources also. Boron has a low thermal expansion and thus is an ideal additive since it reduces the tendency of glazes to craze. Since there are no practical insoluble sources of pure boron, ceramic chemistry is normally needed to determine how to best incorporate boron-sourcing materials.

Out Bound Links

  • (Glossary) Glaze Chemistry

    Glaze chemistry is learning what each oxide does in a fired glaze and the relative advantages and disadvantages of each material supplying it. The chemistry of a glaze is expressed in a manner similar to its recipe, except that the items are oxides and the amounts can be by weight (an analysis) or n...

  • (Articles) G1214M Cone 5-7 20x5 Glossy Base Glaze

    This is a base transparent glaze recipe developed for cone 6. It is known as the 20x5 or 20 by 5 recipe. It is a simple 5 material at 20% each mix and it makes a good home base from which to rationalize adjustments.

  • (Oxides) B2O3 - Boric Oxide
  • (Articles) Reducing the Firing Temperature of a Glaze From Cone 10 to 6

    Moving a cone 10 high temperature glaze down to cone 5-6 can require major surgery on the recipe or the transplantation of the color and surface mechanisms into a similar cone 6 base glaze.

In Bound Links

  • (Glossary) Borosilicate

    A silicate is an SiO2-centric solid (crystalline or glass). A borosilicate simply is a silicate with boron. The term 'borosilicate' is synonymous with medium and low fire glazes because boron is not employed at high temperatures (CaO, Na2O, MgO, etc flux silica and bond with it to form crystalline o...

  • (Typecodes) 3: MTR - [label]
  • (Videos) Reducing the Firing Temperature of a Glaze From Cone 10 to 6

    A key lesson because it explains the difference between cone 10 and 6 glazes, demonstrates how to evaluate frits to choose the best one to source boron to a glaze, how to determine how much frit to ad...


By Tony Hansen




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