#declare PlankNormal =
  normal
  { gradient x 2 slope_map { [0 <0,1>][.05 <1,0>][.95 <1,0>][1 <0,-1>] }
    scale 2
  };

plane
{ y, -.25
  pigment
  { wood color_map
    { [.4 rgb <.9, .7, .4>]
      [.6 rgb <1, .8, .6>]
    }
    turbulence .5
    scale <1, 1, 10>*.5
    rotate y*20
  }
  normal
  { average normal_map
    { [1 PlankNormal]
      [1 wood .5 slope_map { [0 <0,0>][.5 <.5,1>][1 <1,0>] }
         turbulence .5 scale <1, 1, 10>*.5]
    }
    rotate y*20
  }
  finish { specular .5 reflection .2 }
}