We share our classroom with multiple other groups, so each week we set up from scratch in the morning before class, and completely remove everything at the end of class. That means we can’t leave long-term projects in the classroom, so we’ve never been able to do some projects like crystallization. When all our families are at home for weeks, it was the perfect time for long-term projects like sprouting seeds in our connecting to nature unit, and crystallization experiments in our chemistry-at-home unit.

Each crystallization project starts with creating a super-saturated solution of either sugar or salt, and then letting it rest for days while crystals formed. To make a super-saturated solution, you work with hot water, and stir in salt / sugar till it dissolves. Add more salt / sugar and stir… keep doing this till no more will dissolve. For salt it’s a ratio of about 1:1. For sugar, it’s up to 3 parts sugar for 1 part water. Here’s what we tried.

Egg Geodes

Ingredients: Egg shells, food color, iodized table salt or Kosher salt.

Step 1: Take a bowl which is just larger than the eggshell. A glass bowl is better so that you can watch the growing process. Wash the eggshells with warm tap water and then wipe it dry with a paper towel or napkin.

Boil water – enough to fill the bowl you plan to use. When it’s boiling, take it off the heat, then add salt, stir till it dissolves, keep adding salt till no more will dissolve, and salt starts settling out at the bottom of the bowl. For 6 ounces of water, you can add 3 – 4 tablespoons of salt. Add 1 – 3 drops of food coloring. Stir.

Pour the colored salt solution over an eggshell first so that it doesn’t float, and then continue to fill the bowl around the eggshell.

Step 2: Crystallization will start the next day. Wait till water evaporates, and after approximately 6-7 days you will see several crystals have formed.

This experiment was inspired by: https://planningplaytime.com/how-to-grow-crystal-geodes

Rock Candy (Crystallized Sugar)

Ingredients: 1 cup of water, 2 cups of granulated sugar (note: powdered sugar will not work), food color (optional).

Step 1: Clip wooden skewer into the clothespin (a.k.a. cloth peg) and adjust as needed so that the clothespin will rest across the top of the jars and the skewer will hang down on the inside as shown below. We used only one clothespin and skewer per jar but you can use two if you want.

Step 2: Dip the bottom portion of the skewer in water and then roll in granulated sugar. Leave the skewer exposed to air for drying. (Having some crystals on the stick already helps the crystallization process later on.)

Step 3: Boil water in a pan on stove. Add sugar in small amounts and keep stirring until sugar dissolves completely, keeping the solution at a low boil. Keep adding sugar till no more will dissolve. You will use a lot of sugar… perhaps 3 times as much sugar as water. Be very careful, as hot sugar can burn! Set the sugar solution aside to cool completely. (Note: The solution should cool completely for best results)

Step 4: Remove the inverted skewers and pour the sugar solution into the jar, add a few drops of food color (5-6 drops of liquid color) and stir it gently.

Carefully dip the sugar-coated end of the skewer into the jar, resting the clothespin across the mouth of the jar. Be sure they are hanging straight down the middle without touching the sides or each other.

Step 5: Let sit for a week. Then, remove the skewer and let it dry on a plate or in an empty jar for couple of hours. The rock candy is now ready to eat….enjoy!!

Inspired by: https://www.yummymummyclub.ca/blogs/paula-roy-whole-foods-in-half-the-time/20160301/homemade-rock-candy-a-delicious-science

Epsom Salt Crystals

Ingredients: Epsom salt, measuring cup, food color (optional), a glass jar or any other clear tall cup, water, pebble, stirring spoon

Step 1: Heat 1 cup of water in microwave for 45 seconds, add few drops of food color of your choice and stir it with a spoon. Now add Epsom salt in small amounts, stir till it dissolves and keep adding more and stirring till no more salt will dissolve. (Approximately 1 cup of Epsom salt total.)  

Step 2: Drop in a pebble. Crystals need something to grow on and one little impurity in the water like a pebble helps the crystallization start.

Step 3: Place the jar in the freezer for 10 minutes and then move it to the refrigerator. Place it in a location where you won’t have to move it often (to reach other things).  Leave the jar in the refrigerator for 2 days. Then pour off the excess water. Crystals have formed in the jar. (Inspired by https://babbledabbledo.com/science-for-kids-crystal-garden/)

More Salt Crystals!

Boil water. Mix in table salt in at a 1:1 ratio. Then heat the salt water in the microwave for a minute (cover it, or you’ll have salt crystals all over the microwave!). Soak strings in the water, and then let them dry overnight. Let the salt water cool. The next day, tie strings onto straws and lay them across the top of a glass of salt water so the string hangs down into the water. Let sit for several days.

This one was funny – I expected salt crystals on the string under the water – and I got some, but they were light and feathery crystals. Up above the surface of the water, there were big thick chunky crystals on all three strings. And the straw and the top edge of the glass were covered in salt.

Note: I only soaked and dried one of my strings in advance. The other two strings you see were put in dry when the water was still hot. They got a few chunky crystals up top, but didn’t wick the salt up onto the straw like the one that was soaked and dried first.

More Ideas

You can also make sugar geodes. Just search for ideas, or start with this one: https://geekygoblin.blogspot.com/2014/01/sugar-geodes.html. Or search for “geode cake” to see examples of how bakers have used this technique.

Science Note

One of my science advisers said, after reading this post, that “FYI, there is practically no temperature dependence to the solubility of table salt. :)”

So, it’s possible that all the salt experiments might work just as well if you didn’t heat the water before dissolving the salt. Somebody run this experiment, and let me know!