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G2926S - G2926B Reduced COE (MgO)

Modified: 2019-01-18 16:31:02

Low expansion version of Plainsman Clays/Digitalfire G2926B cone 6 clear base glaze

Material Amount
Nepheline Syenite20.13
Ferro Frit 313410.48
Fusion Frit F-6910.31


This is an adjustment to G2926B to reduce its thermal expansion. It increases MgO at the expense of KNaO. Even though MgO levels are quite high, no loss of gloss has happened! The effect on lowering the thermal expansion is dramatic.

This looks very promising. With 10% added zircopax it produces a white of even lower thermal expansion. We have subjected various Plainsman P300 pieces (a difficult-to-fit-glazes-to body) to 300F:IceWater thermal shocking and there is no crazing.

Ferro Frit 3249 can be substituted for Fusion F-69 (although F-69 is more reliable for ceramics). Likely any kaolin can be used.

Although there is only 12.5% kaolin this will suspend well if you follow the same procedure as explained for G2926B. In our initial mix 5000g water and 6000g powder produced 1.47SG. That was very watery so we added about 10g of Epsom salts to gel it.

Related Information

G2926S low expansion cone 6 base glaze is here

G2926B has proven to be my most durable, crystal clear, non-crazing, easy-to-use general purpose cone 6 base glaze (from dozens I developed). However, some porcelains (e.g. Plainsman P300) need an even lower thermal expansion. G2926S adjusts "B" (by adding low-expansion MgO at the expense of high-expansion KNaO). Yet it has the same gloss. The insides of these P300 mugs use it (with 10% added Zircopax to make white). "S" is not an all-purpose recipe, it could shiver on high silica bodies, use it if G2926B fails an IWCT test for crazing. These mugs were fired using the PLC6DS firing schedule, the outside glazes are G2934Y silky matte with added stains.


Recipes G2926B - Cone 6 Whiteware/Porcelain Transparent Base Glaze
A base transparent glaze recipe created by Tony Hansen for Plainsman Clays, it fires high gloss and ultra clear with low melt mobility.

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By Tony Hansen

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