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