The idea is to create a cast iron effect or a rough surface to the plastic. The process uses a solvent glue (I am using Mr Cement Deluxe) other thin solvent glues for model building can also be used; and an old toothbrush. Beginning with a cleaned part (seam lines, mold lines, and spruce nubs have been sanded down). Apply glue to the surface of the parts, the use the brush to rough up the surface of the part. As the glue works against the plastic, melting it; the toothbrush works to get the surface very rough. The plastic parts will be very rough and have some plastic burrs from the brushing process.
The second part to the technique needs to let the glue completely dry and cure before progressing. I usually leave the parts to dry over night to fully cure. Once cured, a medium grit sanding pad is used to remove the rough burrs and bigger rough spots leaving the surface that is textured. The parts can be left alone, or painted at this point.