So. Following on from a previous thread where it was concluded an overnight spider visitor has left its mark (as opposed to a marker pen which is what it looked like), three washes on and the marks are still there on a white cotton duvet cover.
I've just put some concentrated bleach on the marks and left it for about an hour before putting in a 90 degree wash. It didn't look like the bleach had made any difference but we'll see when the cycle is finished.
If it hasn't worked, what on earth else can I try?