G3806C has been our recommended base recipe for reactive glazes (by the addition of colorants and opacifiers). It excels for copper blues, for example. But its thermal expansion is high enough that it crazes on some bodies (e.g. Plainsman P300). To adjust it (via glaze chemistry) I introduced some low expansion Li2O (from Spodumene) at the expense of high expansion KNaO, this dropped the calculated COE from 7.1 to 6.6. The melt fluidity, shown here at cone 6 (its most important feature), is exactly the same. The color is bluer. But not as dark, so copper oxide might be better. Or a higher percentage of copper carbonate. The base recipe (without the copper and tin) is potentially very valuable to create other reactive effects that depend on melt mobility. Why? Because it is very difficult to create a high gloss melt fluid glaze that also has a low thermal expansion.
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.