First measure how much cord you need - it should be the full width of the curtain plus about 30cm, times how ever many rows of cord there are in the header tape (usually 2 or 3). Buy the replacement cord of the same thickness (or a bit thinner) as the old cord and cut it into the right number of lengths. Undo any knots in the ends of the old cord. You could try tying one end of a new length to an end of the old and pulling it through, but the knot is likely to get stuck. Instead, thread a length of the new cord through a bodkin or long darning needle and sew it in and out of the header tape, being careful to go in and out of the same holes as the old cord - pull the old cord out as you go, pulling it from the far end. If the old cord is secured invisibly at the far end, cut it where it first appears on the visible side of the tape. Repeat with the other lengths of cord, knotting the ends together at each end of the curtain but leaving a free length of 20cm or so at one end (the end that will be at the edge of the window) so you have something to hold onto when you pull up the cord before hanging the curtain. Do not cut off the spare cord when you have pulled it up, you need to be able to undo the header tape when you come to wash the curtain.
Yorkshire Lass, May 2009
