Once you have a sheet of clay, you can impress it with anything to hand - crosshead screwdrivers, coarse grit sandpaper and the soles of flip flops have all been used. Here are some commercial textures.
Textures are also used to create multi-coloured patterns. The pink/red patterns were made from the pink/red textures, and the green from the yellow textures, seen above.
Using a variety of cutters and blades, different colours of clay can be cut and recombined into different patterns.
Clay can be used to make canes, 'sausages' of clay where the patterns run right through it. Think sticks of rock, or swiss rolls. The cane is then cut into slices, which are places next to each other to form the pattern, rather like tiling a bathroom.
A piece doesn't have to be smooth - textures can also be created using different shapes and colours, sometimes slices of cane, layered on a base.