For stone ware temperatures the limit formula tables indicate an
Al : Si ratio of around 9 - 10.
the silica level is appropriate for the temperature then the Al
: Si ratio lower than 9 might indicate a move towards a more viscous
and perhaps opaque and matt glaze resulting from excessive Al2O3.
(a higher ratio) might indicate a glaze which tended to move while
still showing opacity resulting from excessive SiO2.