Hosting a sleepover? Pack your child’s overnighter with a fun science craft! Here’s a fun and safe way to grow rock crystals during the night when your child and their buddies catch some ZZZ’s.

The best news about this experiment? It requires alum powder, a safe compound found in the grocery store spice aisle. Not potentially harmful like boric acid, alum powder is salty and commonly used for pickling vegetables. It is also found in cosmetics and natural deodorants, because it can safely be absorbed into the bloodstream.

DIY Overnight Crystal Craft


Step one: The morning of the sleepover, before guests arrive:

Gather your supplies. You will need chenille pipe cleaners, clear glue, food coloring, about 8 ounces of alum powder, string, several one-quart mason jars, an old watercolor paint brush, and items from your kitchen to act as dowels for hanging your crystals (like pencils or a wooden spoon).

DIY Overnight Crystal Craft

In the morning, tie a length of string around the end of a chenille pipe cleaner.

DIY Overnight Crystal Craft

Wrap the chenille pipe cleaner around itself until it forms a little ball.

DIY Overnight Crystals

Grab three more pipe cleaners and wrap those around the small ball. Make as many balls on strings as you would like to have crystals.

Using your dowel from the kitchen, create a station where you can hang your chenille balls. In the next step, you will be covering them with glue, so you want your station ready to go so you can hang them. Make sure there is paper towel and a plate under your dowel.

Next, pour a little bit of glue into a disposable paper cup. Dip the chenille ball in the cup. Grab your paintbrush to coat the balls entirely.

Hang your chenille glue balls from the hanging station you created.

As the ball suspend over the paper towel and plate, sprinkle some alum powder over the balls until they are covered. Let it dry for the day.


Step two: In the evening when your sleepover guests have arrived:

When your child’s guests arrive, immediate intrigue of the hanging pipe cleaner balls will ensue. With your sleepover scientists gathered around, add two cups of boiling water in each of your mason jars (adults only for handling the boiling water!). Then add 40 drops of food coloring and stir.

Have your guests stir in ¾ cups of alum powder into the water, ¼ cup at a time. Stir well each time until it is dissolved.

Tie the dried glue ball to a pencil or wooden spoon. Lower the ball into the Mason jar, placing the pencil on top of the jar. Be sure the string is long enough so the ball will be submerged in the water/alum mixture. The ball should be suspended, not touching the sides of the jar.

DIY Overnight Crystals

Now send your sleepover guests to bed and wait overnight for the magic to happen!

DIY Overnight Crystals

Step three: The morning’s big reveal!

Because of the intense food coloring, throw on some disposable gloves when reaching in to get out the crystals. Rinse them in the sink and dry them with paper towel.

DIY Overnight Crystals

Wow! Your sleepover scientists will be blown away with what has grown overnight! Beautiful, safe, and chemical free rock crystals. A great souvenir from the awesome (and scientific) night at your house!

DIY Overnight Crystal Craft

Happy Sleepover Science!

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DIY Overnight Crystals