Plasticity._ This stems from the size of the par-
ticles and the typology of clayey minerals present. In gen-
eral, an increased plasticity is due to the presence of clayey
minerals in which the layers are weakly bound (minerals
of montomorillonite and/or illite nature), to the reduced
size of the particles, to the low order crystal structure
and to the presence of organic substance (e.g. ball clays).
The plastic clays increase the mechanical resistance in
the green state and hence reduce the defects connected
with all those phases involving mechanical stresses on
unfired tiles (transport, glazing, brushing, etc.).