Pinholes are small holes in the glaze surface where gas bubbles burst through the molten glaze but the glaze failed to flow back and heal the opening before solidifying.
Understanding This Defect
Flux-related causes include: insufficient flux in the glaze (the glaze is too viscous to heal bubble holes — increase nepheline or feldspar content by 3-5%); too rapid firing in the peak temperature zone (the glaze does not have time to mature and degas — extend soak time or reduce peak temperature); and gas generation from body raw materials that continues after the glaze has sealed (use nepheline to lower the vitrification onset temperature so body gas release completes earlier while the glaze is still permeable). Our K200 at 200-mesh has faster dissolution kinetics than 100-mesh grades, promoting earlier and more complete glaze maturation that heals pinholes. For body-originated pinholes, increasing nepheline content by 3-5% accelerates body vitrification, completing gas release before the glaze seals the surface..
Solution & Prevention
