surface
plastic(float Ka = 1, Kd = 0.5, Ks = 0.5;
        float roughness = 0.1;
        color specularcolor = color (1,1,1))
{
    point Nf = faceforward(normalize(N), I);
    point V = normalize(-I);

    Oi = Os;
    Ci = Os * (Cs * (Ka * ambient() + Kd * diffuse(Nf))
         + specularcolor * Ks * specular(Nf, V, roughness));
}