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G2926S - G2926B Reduced COE (MgO)

Modified: 2022-08-30 07:51:29

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

Notes

This is an adjustment to G2926B to reduce its thermal expansion. However, before trying this, we recommend ball milling the G2926B or using 325 mesh silica in that recipe. Only if those do not work, then try this (use 325 silica in this one also, the fine particles assure all of it melts).

This recipe 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.

With 10% added zircopax this 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. However that much zircon can induce crawling issues, we have found that 3% tin and 5% zirocpax is better.

For use as a transparent consider adding 2% zircopax. That is insufficient to opacify but the zircon does act as a fining agent to remove microbubbles and make the glass more transparent.

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 the slurry is thixotropic. 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 liner glaze

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.

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