differing from that of the above mentioned operation or at the same speed when the dryer is an integral part of the kiln the same applies to drying of the glazing in the following description reference is made to a process wherein drying of the tile body is performed previously and separately while drying of the glazing is carried out immediately prior to heating and at the same speed in this case it lasts a few minutes for example from 5 to 7 minutes at suitable temperatures for example up to 200 u00b0 c and under an adequate and intense gas circulation when drying of the glazing is completed and the actual heat treatment starts the temperature of the tiles according to the present invention is quickly raised up to the firing temperature the firing temperature measured near the tiles as are all the temperatures stated in this specification may vary quite substantially according to the compositions but it is generally around 1000 u00b0 c as for example between 800 u00b0 c and 1200 u00b0 c but more commonly between 1000 u00b0 c and 1100 u00b0 c for example around 1050 u00b0 c and 1060 u00b0 c the heating of the tiles is carried out as referred to above in an environment where heat transmission takes place by convection with gas flowing counter current to the direction of travel of the tiles and besides heating the tiles it heats also the walls of the heat treatment chamber which are normally made of refractory.