These cone 6 glazes are the same (G3806G), except the one on the right has 3.5% copper carbonate added. Copper is commonly thought to flux glazes, making them melt more. But in this case it percentage is not high enough, the clear base is running just as much as the stained one. Another observation: I was suspicious that the micro-bubbles in the glass matrix were coming from the copper carbonate gassing during firing. But not so, as you can see, the flow on the left has them also, actually, it has even more.
Ceramic glazes melt and flow according to their chemistry, particle size and mineralogy. Observing and measuring the nature and amount of flow is important in understanding them.
A source of CuO copper oxide used in ceramic glazes to produce a variety of colors (used only or with other colorants).