This glaze creates the opaque-with-clear effect shown (at cone 7R) because it has a highly fluid melt that thins it on contours. It is over fired. On purpose. That comes with consequences. Look at the recipe, it has no clay at all! Clay supplies Al2O3 to glaze melts, it stabilizes it against running off the ware (this glaze is sourcing some Al2O3 from the feldspar, but not enough). That is why 99% of studio glazes contain clay (both to suspend the slurry and stabilize the melt). Clay could likely be added to this to increase the Al2O3 enough so the blisters would be less likely (it would be at the cost of some aesthetics, but likely a compromise is possible). There is another solution: A drop-and-soak firing. See the link below to learn more. One more observation: Look how high the LOI is. Couple that with the high boron, which melts it early, and you have a fluid glaze melt resembling an Aero chocolate bar!
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