isosurface { //-------------------------------------------

  function{
   f_sphere(x/2, y, z, 1.8)
   -f_marble(x*2,y*3,z*3)*0.2 
   //-f_bumps(x*3,y*2,z*3)*0.15
  }

  contained_by { sphere {<0,0,0>,  4.6  } }
  accuracy 0.003
  max_gradient 5

  texture{ pigment{ color rgb<0.3,0.1,0.9>}
           finish { phong 0.4 reflection 0.1}
         }
  scale 0.4
  rotate<0, 30,0>
  translate < -0.2, 1.2, 0>
}// end of isosurface  -----------------------------------