Unity Formula

The chemistry of ceramic glazes are normally expressed as formulas. A unity formula has been retotaled to make the numbers of flux oxides total one.

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Details

A "unity formula" is just an oxide formula that has been retotaled so that the RO group of oxides sums to 1. This is also called a Seger formula. It is a standard that provides one basis for comparing glazes. The three-column format of expressing a formula was first used by Hermann Seger. 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 or inactive in low fire. Oxides have a much more individual presence or depend on interactions (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. Many people prefer to use Mole% when rationalizing how a formula relates to the fired product. However, all of this being said, there is great value in a method of presentation that clearly shows the relationship between Al₂O₃, SiO₂ and everything else.

Some argue that the unity formula method of presenting glazes is not precise enough for glaze chemistry calculations. However, the greatest source of imprecision by far is the accuracy of the analyses of the materials being used. Any method that calculates an exact match for an existing chemistry will also produce an exact match in unity formulas. Unity formulas work better in targeting when doing batch to chemistry calculations because additions or changes in percentage of a material do not always change every number in the formula. However it must be remembered that glaze chemistry is not about precise mathematics, it is comparative and best viewed in context and as a tool to help when comparing one thing with another.

Digitalfire desktop Insight required that users specify whether to unify recipes to RO or R2O₃. However Insight-live automatically sets this (the group having the greater total wins the unity setting). Users can click the 'Auto Unity' heading and it will cycle between various settings, eventually coming back to auto-unity. Recipes remember their settings.

Related Information

The Seger Unity Formula

Ceramic material powders can be crystalline or amorphous (or a combination) and they can be natural or man-made and they can have very different particle physics. Ceramic materials are classic case studies of the sciences of solid state physics and solid state chemistry. Mineral sources of oxides impose their own melting patterns - 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 is sourcing Al₂O₃ to a glaze using calcined alumina instead of kaolin. Although the chemical formula of the glaze may remain unchanged, the fired result would be completely different. This is 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 they readily release their oxides to the melt.

Links

Glossary	Mole% Mole% is a way of expressing the oxide formula of a fired glaze or glass. It is a preferred over the formula by many technicians who use glaze or glass chemistry.
Glossary	Chemical Analysis In ceramics, raw material chemistry is expressed a chemical analyses. This is in contrast to fired glaze chemistries which are expressed as oxide formulas.
Glossary	LOI Loss on Ignition is a number that appears on the data sheets of ceramic materials. It refers to the amount of weight the material loses as it decomposes to release water vapor and various gases during firing.
Glossary	Oxide Formula In ceramics, the chemistry of fired glazes is expressed as an oxide formula. There are direct links between the oxide chemistry and the fired physical properties.
Glossary	Glaze Chemistry Glaze chemistry is the study of how the oxide chemistry of glazes relate to the way they fire. It accounts for color, surface, hardness, texture, melting temperature, thermal expansion, etc.
Media	Desktop Insight 5A - Glaze Formula to Batch Calculations Learn to use a non-unity calculation to convert a formula into a batch recipe using theoretical and real-world materials. Retotal, round-off and make a side-by-side report.
Articles	Glaze Chemistry Basics - Formula, Analysis, Mole%, Unity Part of changing your viewpoint of glazes, from a collection of materials to a collection of oxides, is learning what a formula and analysis are, how conversion between the two is done and how unity and LOI impact this.
Articles	How desktop INSIGHT Deals With Unity, LOI and Formula Weight INSIGHT enables you to enter material analyses as recipes. This is a first step to inserting them into the materials database. Imposing an LOI and understanding how to set unity, and its connection with formula weight are important concepts.

By Tony Hansen
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