//--------------------------------------------------------------------------
// #include "math.inc"  
#declare R= 1;      // radius (of the middle of waveline)
#declare D= 0.075;  // half dent heigth 
#declare Z= 0.2;    // thickness in +z direction               
#declare Ridges=21; // number of dents or waves

isosurface { //---------------------------------- cylinder with wavy outline
  function{ sqrt(x*x+y*y)-R   -  cos(atan2(y,x)*Ridges)*D  }
  threshold 0
  max_gradient 2
  contained_by {box{<-1-D,-1-D,-Z>, <1+D,1+D,Z>}}
  texture { T_Silver_3A
            normal { bumps 0.5 scale 0.0015} 
            finish { phong 1}
          } // end of texture 
  scale 1
  rotate <0, -30, 0>
  translate <0, 1.0, 0>
} // end of isosurface -----------------------------------------------------