Tie the string to your pipe cleaner shape and the other end to a pencil. Rest the pencil across the mouth of the jar so the shape hangs freely in the middle, not touching the bottom or sides.
Once you’ve mastered alum and borax, try: making crystals
Borax crystals are popular because they grow quickly and can be shaped using pipe cleaners. Tie the string to your pipe cleaner shape
Grow Your Own Magic: A Beginner’s Guide to Making Crystals at Home making crystals