The Villeroy & Boch tiles shown are licence products from V&B Fliesen GmbH

Can cracks occur in the glaze?

Yes. These hair-line cracks, which are also referred to as crackling, can occur as a result of tension between the ceramic body and the applied glaze. Tension between the substrate and the tile may also result in this effect.
The products on which hair-line cracks may occur are marked with a corresponding symbol (drinking glass), indicating this possibility of crazing.