Most kilns now are of the tunnel type. As many as 3000 bricks are loaded onto moving carriages which enter the tunnel kiln at the cool end and move slowly forward through progressively increasing temperatures to the firing zone. They pass through it and into decreasing heat zones and emerge cooled. Though suited to mass production, by their very nature the kilns waste a lot of energy through heat losses along the kilns. In bricks the colours are predominantly natural and variations are through differing blends of clay.
Fireclays usually produce the lighter colours such as buff and grey.
Surface clays and shales are associated with the red ranges. Variations on these are achieved by regulating the firing or by the addition of metals such as manganese to the clays at the mixing stages. Applied colours can be achieved by blowing coloured sands onto the column of clay as it moves towards the moulds. Likewise texturing is done in a similar fashion. For glazed wall and floor tiles introduced colours can be held in the glazed surface which is fixed during the firing process.