|Monthly Tech-Tip |
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In 2015 I documented a project comparing common cone 6 fluid-melt base glazes, picked a favourite (Panama Blue) and over-hauled the recipe to fix it's slurry issues and serious crazing. While fluid-melts almost run off ware when applied thick, they host stains & opacifiers to produce brilliant super-gloss surfaces. But the typical chemistry of these is susceptible to crazing, scratching and leaching. In 2019 I reformulated again, moving the thermal expansion down from 7.3 to an incredible 5.8 (the base can now survive a 325F-to-icewater test on our toughest-to-fit porcelain with no crazing). And it is melt-fluidity-controllable, durable (having 30%+ more Al2O3/SiO2) and sources Li2O, MgO and KNaO from frits. Follow the link here to see the entire history of this development effort (beware, there are multiple pages, each with many columns).
This was left for 24 hours. Wrapped in stretch wrap. Then the surface of the glaze was inspected under a lamp to detect any differences between the lemoned and non-lemoned surfaces. Lemons are highly acidic. This glaze passed because the base recipe, G3806N, was methodically developed so that it has plenty of Al2O3 and SiO2 (in the fired chemistry) to build a stable glass.
These tiles are a 50:50 mix of Plainsman L215 and M390. They are fired at cone 1, 2.5 &4 (columns 1,2,3). The glaze is G3806N (v1) with stains at 10% concentrations. That glaze is a fluid-melt for cone 6, but it performs nicely down to cone 1 and even lower. There is no visible crazing and the iron body is stoneware-strength. The firings were only held for 10 minutes at cone (no slow cool). These coloured glazes are also less "muddied" by the iron in the body than would be the case at cone 6. This is a really amazing result. Red-burning bodies can be difficult at cone 6 (if fired too high the red color is lost, if fired too low they are too porous). If you do not have the frit for the N version, try G3806E or G3806F.
G3806C - Cone 6 Clear Fluid-Melt Clear Base Glaze
A base fluid-melt glaze recipe developed by Tony Hansen. With colorant additions it forms reactive melts that variegate and run. It is more resistant to crazing than others.