More copper can produce fewer bubbles!

Saturday 25th July 2015

The first glaze, G2926B, is a standard insight-live.com/glossary/210">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.

Pages that reference this post in the Digitalfire Reference Library:

Copper Carbonate Basic, G3806C - Cone 6 Clear Fluid-Melt transparent glaze, GBMF Glaze Melt Fluidity - Ball Test, Two base clear glazes with 2% copper: One is bubbling and one is not.

This post is one of thousands found in the Digitalfire Reference Database. Most are part of a timeline maintained by Tony Hansen. You can search that timeline on the home page of digitalfire.com.