What are limit formulae?

Unit 7 Topic 1
Using Unity Formula

Limit formulae describe suggested minimum and maximum levels for the molecular parts of glaze oxides in the unity formula at each firing temperature.
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For the flux oxides only maximum levels are given. For alumina and silica minimum and maximum amounts are suggested.

Limit formulae originated from the work of Hermann Seger who established a recipe (unity formula) for his pyrometric cones which softened and bend within specific melting ranges. Seger focused on alumina and silica levels for each cone / temperature while maintaining a consistent flux content in his recipes.

Since that time research has established broad guidelines for flux oxide maximums and for boron.

Some computer software such as MATRIX use graphic displays to display the oxide limits for the firing temperatures.
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Oxide
Mol. Parts
KNO
CaO
0.3
0.7
Al2O3
0.5
SiO2
5.0

Seger's unity formula
for Cone 5

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