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Unity Formula

A "unity formula" is just a formula that has been retotaled so that the RO group of oxides totals one. This is also called a Seger formula and this standard provides one basis for comparing glazes. The three column format of expressing a formula was first used by Hermann Seger. The unity is normally set to the fluxes. Here is how we would recalculate a raw formula to a flux unity:

           Raw              Unity
Oxides Formula Formula
K2O 0.6 / 2.2 = 0.27
CaO 1.3 / 2.2 = 0.59
MgO 0.2 / 2.2 = 0.09
ZnO 0.1 / 2.2 = 0.05
----- ----
Flux Total 2.2 1.0
Al2O3 0.9 / 2.2 = 0.41
SiO2 9.0 / 2.2 = 4.09

The Seger method of rationalizing the chemistry of glazes does not work as well at lower temperatures because some oxides that are powerful fluxes at high temperatures are refractory in low fire. Oxides have a much more individual presence (at each temperature range) than the Seger method tends to recognize. Also, their contributions to particular properties often are not linear according to concentration. For example, boron is both a glass and a flux and the logic for its employment at various temperature ranges differs. It does not 'plug into' a Seger formula well. For these are other reasons, many people prefer to use Mole%.

Digitalfire desktop Insight required that users specify whether to unify materials or RO or R2O3. However Insight-live automatically sets this (the greater of the total of the two sets that one to unity).

A Limitation of the Seger Unity Formula

Mineral sources of oxides impose their own melting patterns and when one is substituted for another to supply an oxide a different system with its own relative chemistry is entered. An extreme example of this would be to source Al2O3 to a glaze using calcined alumina instead of kaolin. Although the formula may be exactly the same, the fired result would be completely different because very little of the alumina would dissolve into the glaze melt. At the opposite extreme, a different frit could be used to supply a set of oxides (while maintaining the overall chemistry of the glaze) and the fired result would be much more chemically predictable. Why? Because the readily and release their oxides the the melt.

In Bound Links

  • (Glossary) Mole%

    Mole% is a way of expressing the oxide formula of ...

  • (Glossary) Analysis

    Conceptually we consider fired glazes as being com...

  • (Glossary) LOI

    Simplistically, LOI is the percentage of weight a ...

  • (Glossary) Formula

    Conceptually we consider fired ceramic glazes as b...

  • (Videos) Lesson 5A - Glaze Formula to Batch Calculations - D. Desktop Insight

    Shows you how to use a non-unity calculation and t...

By Tony Hansen

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