Abstract: A process and apparatus for forming a wood grain simulation pattern on surfaces of synthetic articles such as synthetic lumber planks. The articles are fed along a predetermined path on a conveyor surface. A plurality of cutting blades are disposed about the periphery of a rotatable cylindrical element supported on a drive shaft. As the synthetic article is fed under the rotatable cylindrical element which is in rotation, the blades which are disposed across an outer surface of the article on which a grain simulation is desired, cut a plurality of short slits spaced laterally from one another in an offset pattern. These slits extend along the feed axis of the article and simulate a wood grain in the outer surface thereof.