Superficial halos formation during the drying process

In ceramic, the drying process takes place inside dryers where raw tiles are placed on metal supports (roller stands) for a preset time, until the residual humidity's percentage is close to 0%.The heating to which the ceramic body is subjected leads to a migration of the water molecules and so to their evaporation.Sometimes this process can be not completely homogeneous over the entire surface of the tile. More precisely: the parts of the ceramic body that rest on the basket rollers may have different evaporation times compared to those areas of the tile that are not in contact with the metal parts of the dryer.This different evaporation process can sometimes produce striped halos on the surface that may remain visible even after the drying cycle. What are the reasons and the mechanisms of the problem and what kind of actions must be previously take to avoid it?