These crystals are made from a super-absorbent polyacrylamide polymer. Placed in water they absorb many hundreds of times their own weight and become virtually invisible. Tie a thread around an expanded crystal, drop it into a glass of water and your crystal seems to disappear! For an additional effect, push a toothpick through the suspended gel. The toothpick seems to mysteriously float in the center of the suspended loop of thread. The index of refraction of the expanded crystals is almost identical to that of water. Can be colored by placing them in a mixture of water and food coloring.