A method of treating the surface of a rough, plastic object to produce a high gloss, textured and/or coloured finish. A rapid prototype treated according to the present method assumes the appearance of an injection molded part, without the usual high costs associated with producing the injection mold. In one embodiment, first step involves of removing the pores in the porous part, at least at the outer layers of the part, followed by a smoothening process of filling the voids between the miniature steps with a hardener to give a smooth surface, on which further post-processing may be performed.