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Zero3 H High Expansion Variant

Code: G2931H
Modification Date: 2017-10-24 10:43:52

Ferro Frit 319530.0
Ferro Frit 313433.0
Ferro Frit 32490.0
Ferro Frit 311017.0


This is a high-expansion version of the Zero3 Clear glaze (code G2931K), originally developed from the Worthington Clear Gerstley Borate based recipe. While G2931K fits the vitreous Zero3 porcelain and stoneware and also non-vitreous low-talc bodies (like Plainsman L212, L215), it shivers on high-talc bodies (e.g. Plainsman L213). That means that this G2931K variant is the most similar to commercial low fire glazes (which are designed to fit high-talc bodies).

This version increases the thermal expansion of Zero3 K glaze from 7.4 to 8.0 (by adding increasing KNaO at the expense of MgO, ZnO).

Do not try to use this with too little water. Mix it to 1.43 specific gravity and add vinegar or Epsom salts to gel it so that it stops moving (after vigorous stirring) in 2 or 3 seconds. When mixed right it applies very well to low or high porosity bisque (in a very thin layer if needed), it does not drip or move.

The soak:soak:slowdrop firing schedule is critical to a defect-free surface.

Three low fire bodies need three different clear glazes. Why?

Three low fire bodies need three different clear glazes. Why?

Glaze fit. The left-most clay mug contains no talc (Plainsman Buffstone), the centre one about 25% talc (L212) and the right one is about 45% talc (L213). Talc raises thermal expansion. The centre glaze is G2931K, it is middle-of-the-road thermal expansion (Insight-live reports it as 7.4) and fits the low-talc bodies (and Zero3 porcelain and stoneware). But it crazes on Buffstone and shivers on L213. The lesson is: Forget about expecting one clear or base glaze to fit all low fire bodies. But there is a solution. I adjusted it to reduce its expansion to work on zero-talc porous bodies and raise it to work on high talc bodies. How? By decreasing and increasing the KNaO (in relation to other fluxes). The three fire crystal clear and work the best in a drop-and-hold firing.

Out Bound Links

In Bound Links

XML to Paste Into Insight

<?xml version="1.0"?>
<recipes version="1.0" encoding="UTF-8">
<recipe name="Ulexite High Expansion Zero3 Clear Glaze" keywords="A cone 04-02 clear glaze developed from Worthington Clear. This employs Ulexite instead of Gerstley Borate and has a lower thermal expansion." id="131" date="2017-09-17" codenum="G2931H">
<recipeline material="Ferro Frit 3195" amount="30.000" unitabbr="KG" added="0"/>
<recipeline material="Ferro Frit 3134" amount="33.000" unitabbr="KG" added="0"/>
<recipeline material="EPK" amount="20.000" unitabbr="KG" added="0"/>
<recipeline material="Ferro Frit 3249" amount="0.000" unitabbr="KG" added="0"/>
<recipeline material="Ferro Frit 3110" amount="17.000" unitabbr="KG" added="0"/>
<url url="" descrip="Recipe page at"/>

By Tony Hansen

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