What changes to the flux group lower the maturing range of a glaze?

Unit 7 Topic 6
Using Unity Formula

A strong flux (e.g. KNO) might be increased or an additional strong flux such as Li2O may be added while reducing a weaker flux (e.g. MgO).
.

It should be remembered that when making changes to flux oxides in a unity formula the unity of the flux group must be maintained i.e. the flux oxide values must total one.

Changing Sandy's Clear from C.12 to C.10 by increasing the power of the flux group.

If the KNO in Sandy's clear is increased by 0.05 then 0.05 in total must be removed from other oxides in the flux group e.g. 0.05 could be removed from the MgO.

Sandy's Clear

Oxide
Mol. Parts
New Formula
KNO
CaO
MgO
0.20 + 0.05 =
0.54
0.26 - 0.05 =
0.25
0.54
0.21
Al2O3
0.50
0.50
SiO2
4.38
4.38
Al : Si
Expan.
8.83
6.86
8.83
7.14

KNO value is increased and the MgO value is
reduced by the same amount to maintain unity.

Instead of increasing the KNO as in the example above 0.05 mols of LiO2 might be added again reducing the MgO by the same amount.

Another technique involves the addition of B2O3. Although not technically a flux replacing some of the SiO2 with this oxide will reduce the maturing range of a glaze and can have other beneficial effects.

After the changes are made to the unity formula the formula can be converted back to a recipe using formula-to-recipe processes in glaze software.

Note:Changing the values in the flux group may have undesirable side effects e.g.

  • in the example above increasing the KNO value increased the coefficient of expansion which would induce more crazing.
  • changing flux content may directly effect response to colouring oxides.
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