Thistle Sack or Finch Sock (call it what you will), this sturdy 18" black nylon mesh sock is the perfect way to start feeding finches.  Larger size for more birds and less filling.  Add a generous pound of niger / nyjer seed and watch the finches go to town, clinging to the mesh fabric in large numbers.  The black sock looks better than white when filled with niger, and the finches show up better!