This is not just a typical transparent cone 6 glaze with 2% copper carbonate added (and 2.5% tin oxide). Knowing what is different about this clear base, its trade-offs and how it was developed are important. The porcelains are Plainsman P300 and M370. The liner glaze is G2926B, it is a gloss but has a much lower melt fluidity than the outer glaze, G3806C (as a functional transparent its main job is to fit the body and be hard and durable). But in order for that outer glaze to accommodate the copper and still be super glossy it must have a much higher melt fluidity. It was tricky to develop since that fluidity comes with high sodium and lower silica, that raises the thermal expansion and moves it toward crazing.
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.
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.