I quite literally can't get enough of crotcheting with string at the moment, there's something that's beautifully old-school and utility about it. Here's a little pattern for a little bottle that I did at the beautiful Butler's Emporium this morning. It would work beautifully scaled up on old jam jars I think...
Free jar/bottle cover crochet pattern
1. mr 6 - 6
2. 2 sc in each stitch - 12
3. *2 sc, 1 sc* repeat to end of row - 18
4. sc until you get to a height you like
5. sl st and thread in ends
6. use hook to weave in ribbon through the top row