Fired at cone 6. A melt fluidity comparison (behind) shows the G3808A clear base is much more melt fluid. While G2926B is a very good crystal clear by itself (and with some colorants), with 2% added copper oxide, it is unable to heal all the surface defects (caused by the escaping gases as the copper decomposes). But G3808A is melt fluid enough to do so. Because copper blue and green glazes need such base recipes, strategies are needed to avoid them running off the ware. That can involve thinner application, use on more horizontal surfaces, use away from the lower parts of verticals or a catcher glaze.

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The first glaze, G2926B, is a standard functional transparent glaze with added copper. The other three are part of a project to find a copper blue (G3806B has the best color and the best compromise of flow and bubble-clearing ability).
The GLFL testers for melt flow are at the back, and the GBMF test melt-down-balls contain 1% copper carbonate. The glazed samples in front have 2% copper carbonate. But why do the recipes containing half the amount of copper have far more bubbles? Because they are thinner? Not really; in use on ware, they also have fewer bubbles. Why? A small CuO addition can change where and how bubbles nucleate and how viscous the melt is. At some point between 1% and 2%, a threshold is crossed that affects nucleation and coalescence. For example, a little copper could encourage lots of tiny bubbles to form and stay trapped, while more changes the melt chemistry enough that they coalesce and escape (or simply aren’t nucleated the same way). Phase separation could produce Cu-rich droplets that enable copper to be its own fining agent.
| Materials |
Copper Oxide Black
The purest source of CuO copper oxide pigment used in ceramic glazes. |
| Recipes |
G3806C - Cone 6 Clear Fluid-Melt transparent 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. |
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