Blisters is a common enamel defect, which is characterized by appearance of circular holes & bubbles in a cooled enameled surface.
May occur as a group, cluster or line of blisters.
Blisters are typically caused by gas evolution during firing, as a consequence of :
- Poor steel quality
- Scratches or damage on base steel
- Large welding seams
- Insufficient cleaning
- Over pickling
- Over blasting
- Impurities in enamel
- Too thick enamel film
- Too high viscous frits
- Contamination of furnace atmosphere
- Under firing