Dorset Buttons

I have just made my very first Dorset buttons... google it...  Although they aren't too bad for a first attempt I discovered that I should have used firmer rings.  In my stash I have loads of rubber O Rings. I thought they would make a good base but in fact they pull out of shape very easily.  I think that I have some small curtain rings in my stash so am planning to give them a try this afternoon. The O rings will probably be ok once I have mastered the tension.