Basically, the clay determines the general final colour of a brick. The interplay of colours is obtained through the firing process and the varying movement of the flames. Contact with combustible materials through the stokeholes in the fire place of the clamp brick and circular kiln after the traditional manufacturing process with coal, charcoal or turf leads to particularly beautiful interplays of colours, the only drawback being that slag and coal residue melt with the brick surface.