Disappearing Ghost Crystals

Suitable for kids aged 5+ with parental supervision.

CAUTION
Ghost crystals are generally considered non-toxic and are safe for use around young children unless ingested. If ghost crystals are swallowed do not give liquids. Seek medical advice.

You Need:

• Water absorbing crystals (available from your local nursery or garden supply centre)
• Transparent cup, beaker or glass
• Water
• Food colouring (optional)

What to do:

1. Sprinkle a small amount of water absorbing crystals into a glass. You don’t need many – a flat teaspoon is plenty.
2. Half fill the glass with water.
3. Now watch. Your crystals will start grow as they absorb water. After a minute or so you will start to notice a difference in their size. Continue to monitor their growth at regular intervals. After 2 hours they will have fully grown.
4. Take out a couple of crystals and investigate the change in their texture (now gel-like) and size.
5. Fill the cup with water and watch the ghost crystals magically disappear. You may need to tip the crystals into a larger transparent glass to see them disappear completely.
6. Drain the water and watch the crystals mysteriously reappear.
7. Drain most of the water and place a few crystals on a paper towel. Leave them in the sun and monitor their decrease in size at regular intervals. They are re-usable!
8. Try sprinkling some salt on the jelly-like crystals. What happens?
9. Try growing some crystals in water with food colouring for a colourful effect.

Ghost crystals are made from a cross-linked polyacrylamide polymer allowing them to absorb so much water (95%) that they have the exact refractivity (how much light is bent) as water, and thus seem to disappear completely in water. They grow up to 200 x their original size in water. Ghost crystals have many real life applications. They are used in agriculture to retain water in soil, in horticulture and mining. They are also similar to the super absorbent polymer used in baby nappies.