What unity formula factors suggest that a glaze will be opaque and textured?

Unit 7 Topic 10
Using Unity Formula

Any movement away from a clear glass balance will promote opacity and texture. Excessive amounts of any of the oxides in the unity formula or an alumina : silica ratio that varies markedly from 1 : 9 will generate opacity and texture.

When compared with the limits for the temperature, excessive flux values in the formula indicate that molecules of the excessive flux will not be able to find SiO2 and Al2O3 molecules with which to combine to form glass. These molecules will precipitate and crystallize on cooling to created opacity and texture.

If there is insufficient SiO2 and Al2O3 appropriate for the firing temperature (even though the ratio may be around 1 : 9) there will be flux oxides left out of the glass fusion.

An Al : Si ratio above 1:9 indicates excessive SiO2 which may give a glaze tending to white opaque and shiny though textured.

A low ratio of alumina : silica (i.e. below 1 : 9) indicates excessive Al2O3 which may result in opaque greyish matt glazes at stoneware temperatures (alumina matts).

Where all flux oxides combine with all the available alumina and silica oxides clear glass is the result.

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