I feel if you're willing to put the time in to make that block, I wouldn't be willing to jeopardize it by using fabric that is not suitable. Go to Wal-Mart and buy a yard at $2.00 and have a finished piece you'll be proud of. Nothing worse than putting in all the work to have a piece you don't like and that won't hold up by the time you're finished. Free doesn't always mean it's ok to use. A quilt is an investment...not just of money, but love and your time. Keep plugging. You learn something new everyday and never have all the answers. That's why we have this forum..it's wonderful!!!