Growing crystals – sugar

We tried this crystal growing experiment from About.com but modified it slightly for our purposes.

Materials:

  • 1/2 cup water
  • 1 cup table sugar (sucrose.  Note:  we were out of regular granulated sugar and ended up using a baker’s sugar which is superfine sugar)
  • clean glass jar
  • pencil
  • rough string (cooking twine works great)
  • pan or bowl for boiling water and making solution
  • spoon
  • stove

Time needed:

Prep time ~ 20 minutes
Crystal growing time ~ A few days to a week.

Caution: Please note young children will require the help of and adult to use the use of a stove and pour the hot sugar solution into the jar.

Method:

Step 1. Tie a length of cooking twine onto a pencil that will be long enough to reach almost the bottom of your glass jar.

Step 2. Make a saturated sugar solution by boiling the water in the pan, slowly adding sugar a teaspoon at a time.  Stir after each spoonful and keep adding sugar until the sugar won’t dissolve any more in the water.  If you don’t add enough sugar, your crystals will not grow quickly.  If you use too much sugar, your crystals will grow on the undissolved crystals and not on the string.

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For us, it was hard to tell when the sugar wouldn’t dissolve anymore, and it’s possible that using the baker’s sugar made it harder to tell.

Step 3. Pour your solution into the clear glass jar. If you have undissolved sugar at the bottom of your container, avoid getting it in the jar.

Step 4. Drape your sting inside the glass jar.

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Tip: It wasn’t until after I did this that I realized we should have weighted our string with something heavy (and preferably edible), like a lifesaver. You don’t want the string touching the sides or bottom of the jar and you do want it covered in the sugar solution.

I realized that I made a super incredibly saturated sugar solution because the sugar started crystallizing within a half hour, forming a crunchy layer at the top of the sugar solution.

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It turns out that this is okay. It just means that you will have to break through the crystal layers to get to your string. But it also means that you will probably have super fast growing sugar crystals.

Step 5. Set the jar aside and check on your string each day and observe the crystal growth. You can cover it with a coffee filter or paper towel to keep dust of of the jar.

This is what it looked like about a few hours after we started:

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And this is what it looked like 24 hours later:

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Step 6. Allow the crystals grow until they have reached size you desire or have stopped growing. You can pull the string out and allow the crystals to dry. You can eat them or keep them.

To download or print this experiment,click on the download or print button on the image below:

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2 Responses to Growing crystals – sugar

  1. Kristin says:

    I just found your fantastic blog. I love doing science stuff with my kids. I’m posting about a sugar crystal growing project we did and linking to you on Monday. (I needed to send readers somewhere with clear instructions and yours are fantastic, I wish I’d found them before we did ours). I’m looking forward to checking out your site, I love science + kids! Thanks for the resource.

  2. Rob says:

    Great recipe! You can use the microwave to save time.
    1 cup sugar, half a cup of water in a 2 cup Pyrex measuring cup, nuke it for 2 minutes (or until the solution boils). Take it out and stir it a bit to make sure the last of the sugar is dissolved. You can also stir in food coloring. You have a nice thick sugar syrup, perfect for crystal growing. Pour it into the crystal growing jar.
    By the way, this is also the recipe (without the color) for “simple syrup”, an ingredient in many cocktails!

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