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By itself, without copper, the G2926B recipe (right) produces a better and more durable glass (comparing the cups in the back). But a 2% copper addition, front, turns its surface to a mass of unhealed bubble-escapes. The G3808A recipe, on the left, develops much more melt fluidity, the extra mobility enables the bubbles, created by the decomposing copper, to coalesce, grow, break at the surface and heal before the melt stiffens too much.

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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 (L3806B has the best color and the best compromise of flow and bubble-clearing ability).
The GLFL testers for melt flow 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.
| Glossary |
Leaching
Ceramic glazes can leach heavy metals into food and drink. This subject is not complex, there are many things anyone can do to deal with this issue |
| Glossary |
Fluid Melt Glazes
Fluid melt glazes and over-melting, over fired, to the point that they run down off ware. This feature enables the development of super-floss and cyrstallization. |
| Glossary |
Transparent Glazes
Every glossy ceramic glaze is actually a base transparent with added opacifiers and colorants. So understand how to make a good transparent, then build other glazes on it. |
| Glossary |
Base Glaze
Understand your a glaze and learn how to adjust and improve it. Build others from that. We have bases for low, medium and high fire. |
| 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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