An apparatus including a first device which moves a first portion of a soft, damp, slightly pressed slab out of alignment with a majority of the slab and thus introduces a first crack in the slab; and a device for spraying a first colored material into the first crack of the slab. The first device which moves the first portion of the slab out of alignment with the rest of the slab may include a first cylinder. The device for spraying the first colored material in the first crack of the slab may include a robotic apparatus. In at least one embodiment, the apparatus may also include a second device which moves a second portion of the slab out of alignment with the majority of the slab and thereby introduces a second crack in the slab.