k3d/share/shaders/k3d_rustymetal.sl:16: *   rustbump - controls the "bumpiness" of the rusty areas.
k3d/share/shaders/k3d_rustymetal.sl:49:	    float rustbump = 0.035;
k3d/share/shaders/k3d_rustymetal.sl:72:  Nrust = calculatenormal (P + rustbump * snoise(PP) * normalize(N));
