 A defect that appears as irregular, bare patches of fired body showing through the glaze where it has failed to adhere to or wet the body on firing.The cause is a weak bond between glaze and body; this may result from greasy patches or dust on the surface of the biscuit ware or from shrinkage of the applied glaze slip during drying.The fault is more likely to occur with once-fired ware such as sanitaryware.