Computer graphics researchers have recently revealed that the presence of imperfections is an essential part of the illusion of photorealism. An improved model to simulate the rust development of ferrous metals in seawater is proposed. The tide and the current, under the gravity of the sun and the moon, affect the stability of the environment at the bottom of the ocean. A simple current model is employed to elucidate the periodic transition of currents in the ocean. L-systems, coupled with the current model, modulate the diffusion of rust according to tendencies based on the object geometry and environmental factors. Changing the underlying distributions of tendency allows images of a variety of metallic rusts to be generated.