The same glaze on both pieces. Fired in the same kiln at cone 6. Both are porcelains, but the one on the right is far more vitreous (it fires off-white so coloured glazes lose some of their brightness). The body is so vitreous that there is considerable interaction between it and the glaze, enough diffusion occurs to affect the surface character.
In ceramics, the zone of adherence between glaze to the underlying body is called the clay-glaze interface. The integrity of this interface is important to strength and functionality.
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