Pinholing is often related to the smoothness of the underlying body surface. The lower half of this vase was tooled during the leather hard stage, all the pinholes occur there. Even though this glaze contains 10% grog, the pinholes are not appearing on the upper half because the slip generated during throwing has left a smooth surface.
Pinholing is a common surface defect that occurs with ceramic glazes. The problem emerges from the kiln and can occur erratically in production.
Glaze Pinholes, Pitting
Analyze the causes of ceramic glaze pinholing and pitting so your fix is dealing with the real issues, not a symptom.