// set a color of the background (sky)
background { color rgb <0.5, 0.7, 1> }

camera {
  location  <0.0, 2.0, -20.0>
  look_at   <0.0, 0.0,  1.0>
  right     x*image_width/image_height
}

          // create a regular point light source
light_source {
  0*x                  // light's position (translated below)
  color rgb <1,1,1>    // light's color
  translate <0, 10, -20>
}

// create a isosurface object - the equipotential surface
// of a 3D math function f(x, y, z)
#declare fn_X = function(x,y,z,tau) { 8*(x^2-tau^4*y^2)*(y^2-tau^4*z^2)*(z^2-tau^4*x^2)*(x^4+y^4+z^4-2*(x^2*y^2+y^2*z^2+z^2*x^2))+(3+5*tau)*(x^2+y^2+z^2-1)^2*(x^2+y^2+z^2-(2-tau))^2 }  
      
      
isosurface {

 function { fn_X(x, y, z,(1+sqrt(5))/2) }        // alternative declared function
  contained_by { sphere { 0, 3 } }  // container shape
  accuracy 0.001                      // accuracy of calculation [0.001]

  max_gradient 3445031.481                      // maximum gradient the function can have [1.1]
// evaluate 1, 1.2, 0.99             // evaluate the maximum gradient
 open 
 material {
   texture {
     pigment { color rgb <0.2, 0.7, 0.2> }
     finish {
       ambient 0.3          // ambient surface reflection color [0.1]          
       diffuse 0.6          // amount [0.6]
       phong 0.5          // amount [0.0]
       phong_size 40      // (1.0..250+) (dull->highly polished) [40]
    
       reflection {
      //0.0                      // minimal reflection value (for variable reflection)
      1.0                        // reflection amount (maximum for variable reflection)
        fresnel on               // realistic variable reflection
        falloff 1.0              // falloff exponent for variable reflection
        exponent 1.0             // influence surface reflection characteristic
        metallic 1.0             // tint reflection in surface color
      }
    }
  }

 }        
  rotate y*30
  scale 3
}