Welcome to our second annual 12 Days of Christmas series. To read all the post in this series visit the 12 Days of Christmas 2017 page.
I remember making Christmas tree ornaments as a kid. In fact, I still have a bunch of them! I loved making them, and now as an adult, I love the memories attached to each and every one. Because of this, I knew I wanted to make ornaments with my kids. But you know what would make it an even better memory? Adding some STEM of course! This is a great activity to learn about chemical reactions and make a homemade ornament for your Christmas tree. Here is how to make milk and vinegar plastic ornaments.
Making the Ornament
This is for one ornament. You can scale the recipe up as needed. (Double it for two ornaments, triple it for three, etc.)
Take 1 cup of milk and bring it to a boil. We used the microwave because I don’t like my son standing over our gas stove, but any method works. Once the milk is boiling dump in 1/2 a cup of vinegar. Then stir!! Very quickly you should see tiny solids forming in the solution. The keys to this reaction are very hot milk and lots of vinegar. If you don’t see any solids formed add more vinegar.
Once the milk has started to cool and you see solids forming, spoon the mixture into a strainer lined with a coffee filter. (A paper towel will work as well, but it might take a bit longer.) You can discard the liquid as it comes out. The solid you have left is your plastic! Once the liquid appears to be out, place a light weight onto the solids to squeeze out every last drop you can. I put one of the kids’ bowls on top with a water bottle. Let that sit for a few hours.
After the liquid is squeezed out it is time to shape your ornament. Use your hands to gently squeeze out any additional liquid with a paper towel. (Seriously, a lot can hide out in there.) Then put the blob of plastic onto a piece of wax paper. Roll it gently out flat. We used cookie cutters to make our ornaments, but you can freehand the shapes too. Once we had our shape I used an additional piece of wax paper to smooth out the top of the ornament. Use a straw to make a hole towards the top so you can hang the ornament when it is done.
I have a few important tips for this shaping step. Don’t make the ornament too thin or it will crack as it dries. It needs to be at least a quarter-inch thick to really stay together. You want to get as much liquid out of it as you can. This both helps the plastic stick together better and shortens the overall dry time. It will be a bit delicate while it dries. So once it is shaped try not to move it!
The ornament needs to sit for about three days to dry fully. I put paper towels over it to help soak up any more liquid. Change them as needed. After about the first day you should be able to gently flip your ornament to help it dry evenly.
The Science Behind the Plastic
This activity is a great example of a chemical reaction. Milk contains proteins called casein, and these are negatively charged. The vinegar contains positively charged hydrogen ions. These two things are attracted to each other and clump together to form the solids you see. This is also a great activity to talk about the differences in properties between solids and liquids!
Want more preschool science fun? Check out my free printables for ready to go worksheets!
Time for Art!
Once your ornaments are dry you are ready to paint them! I put a base coat of paint on ours. I have read that this plastic will never smell. But just in case I wanted to make sure it was sealed. Older kids can do this themselves, but I know my son’s short attention span for crafts so I took care of it.
Then I let my son paint them as he wanted! And I think they turned out great. Add a string, pipe cleaner, or hook and you are ready to go!
These ornaments are a great addition to your tree, or they can make a great gift! This is the perfect project to add some STEAM to your holiday fun.
Kim blogs at Team-Cartwright.com. She is the mom of 3: a 4-year-old son and 1-year-old identical twin daughters. She blogs about parenting, life with twins (+1!), STEM with kids, and the bookkeeping of blogging. You can follow her on Facebook and Pinterest.