Once the temperature of 1200 ◦C was reached, the open (i.e.
apparent) porosity remained virtually negligible, unlike what
has been observed for other materials, such as glass cullet, when
using foaming agents, in which the apparent porosity increases
with processing temperature.This difference could be however
related the much lower amount of total porosity present in
the porcelain tiles, in comparison to glass foams. A higher processing
temperature might still lead to pieces with open porosity,
because of the lower viscosity in the pyroplastic mass leading
to pore coalescence and expansion.