Uniform colouration is no longer acceptable for facing bricks and paving clinkers. The market demands a wide variation in colour as well as surface design. For this reason, reduction firing in a tunnel kiln is becoming increasingly popular because oxidation during the firing process does not allow as much variability in colour as reduction. Multiple colours can be achieved by inner or self-reduction, flash firing, periodic reduction, and permanent or continuous reduction. Each process and its characteristics are described.