The black core is a localized area marked by a brown/black (or even white) color, clearly visible in the thickness of the final ceramic tile.

Its presence is usually a sign of inadequate oxidation, but it has not to be considered a defect that compromises the product functionality (unless the black core comes with a swelling).

The roots of the problem are usually due to some components (both organic and inorganic) that – before the sintering process – do not properly leave the tile by evaporation, since they do not find in the central area of the tile the chemical-physical conditions to uniformly react, such as in the rest of the ceramic body.

The improper expulsion of the organic materials is mainly due to very short firing times.