This is a cone 10R copper red. First, it is thick. "Thick" brings it own issues (like running, blisters, crazing). But look what is under the surface. Bubbles. They are coming out of that body (it is not vitreous, still maturing and generating them in the process). The bubbles are bringing patches of the yellow glass below into the red above. Normally bubbles are a problem, but in this decorative glaze, as long as everything goes well, they are a friend.
In ceramics, reactive glazes have variegated surfaces that are a product of more melt fluidity and the presence of opacifiers, crystallizers and phase changers.
Suspended micro-bubbles in ceramic glazes affect their transparency and depth. Sometimes they add to to aesthetics. Often not. What causes them and what to do to remove them.
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