Apparently invisible. Chemistry in ceramics.

The black core is a localized area marked by a brown/black (or even white) color, clearly visible in the thickness of the ceramic tile.
Its presence is usually sign of inadequate oxidation and it has not to be considered as a defect that compromises the product functionality.
However it's a very serious aesthetic problem, especially if we consider the increasingly different intended use of ceramics.
The origins of this particular defect are many and, according to the specific production conditions, even the actions and solutions to reduce or prevent it can be different.
The episode focuses exactly on this topic, offering a journey that starts at the origins of the problem,and then ending with a range of possible interventions.

After introducing the topic in the previous episode and getting into the details of the problems that may arise before the inkjet application, this new episode focuses on the repellency phenomena that occur after the digital printing process at the interface between the solvent-based inks and the subsequent watery applications of glaze or grit suspensions.
The different chemical nature of the inks (non polar polymers) and all the water-based suspensions (polar), is the basis of the critical issue and it basically results in a incompatibility between the two applications due to a lack of interaction. Just like between water and oil.
The episode looks closer at the mechanisms behind the phenomenon, offering some effective actions to avoid or reduce it.

The ink-jet decoration - that has replaced traditional decoration systems - has removed several problems bringing out, however, new and more complex critical issues.
The new scenario has forced a different attention to all those applications that occur along the glazing line both before and after the digital printing process.
In particular, the different nature of the solvent-based inks, with respect to all the water-based applications of the glazing line (engobes, glazes, grits, etc.), often leads to repellency phenomena that can compromise the proper printing process. In addition, the glaze applied as a final protection (on the ink), when not accurately mixed with proper chemicals, may lead to excessive or low drainage, or even to phenomena of inhomogeneous ink's absorption.
What kind of action must be taken in all these cases? What are the PRIMERS usually involved and how do they work?

The ceramic mixture usually used in ceramic production, largely consists of inorganic raw materials (clay, feldspar, sand, etc.), grinding water and chemical.
These mixtures, since they must be properly managed in the various stages of the production process - from grinding to pressing (or forming) - must be marked by specific and particular features.
In addition to this, the raw ceramic material, once it has been pressed, must have the right properties to prevent and avoid the problems that may occur along the lines (before entering the kilns) and to develop ceramic surfaces without aesthetic or technical defects.
To do this, the use of specific chemicals is a must.
What are the main chemical categories involved and added to ceramic mixtures?
What role do they play and what kind of actions do they promote?

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?