A function for scaling font sizes.

scale-font-sizes.scss

// A function for scaling font sizes.
@function scale-font-sizes($font-sizes, $scale: 1) {
  // A list for holding scaled font sizes.
  $ret: ();

  // Populate the list by mulitplying each font size by a $scale
  // and append it to the end of the list.
  @each $font-size in $font-sizes {
    $ret: append($ret, $font-size * $scale);
  }

  // return our list of scaled font sizes.
  @return $ret;
}

Usage:

  $hf: 10px, 20px, 30px, 40px, 50px, 60px;
  $shf: scale-font-sizes($hf, .9);