The Science of Soap Making

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Glycerin soap figurine.

Learning Objectives: To be able to describe and demonstrate how the melting point of glycerin base can be utilized to make bar soaps.

While we are on the topic of melting stuff to make cool things, let’s explore how to make soap. Soap can be a wonderful item to gift to a family member or friend.  Also soap can be made according to one’s own tastes, allowing for much creativity.   One of my children gave homemade soap to a family member for a birthday present. This individual was really impressed. Also, for a birthday party I made the fish-in-a-bag soap as a favor (see link below). The kids thought it was neat and that it looked like their own pet fish.

Soap making should be performed under adult supervision for younger children, as it does involve heating materials. A simple way to make soap is to melt and pour glycerin base, which you can buy at a craft store such as Michaels or online. The glycerin comes packaged in  blocks. In my town a block of glycerin costs around $10.

Additional items to purchase from a craft store are a soap mold and some soap dyes. Usually you can find these right next to the glycerin in the store. You can use other molds, but the important thing is that you are able to remove the soap from the mold once it is finished.  Applying a bit of vegetable oil to the mold with a napkin before pouring the soap base can help the removal process go more smoothly.

You will also need other supplies that you can typically find at the dollar store: rubbing alcohol (isopropyl alcohol), a spray bottle in which to place the rubbing alcohol,  a microwaveable glass measuring cup or similar microwaveable container with a handle capable of pouring hot liquid, and a stirrer-wood ones work nicely. A spritz or two of rubbing alcohol is used to eliminate bubbles that form from the heating and pouring process.

So, what is the science behind soap making?  Like crayons, the glycerin soap base changes from solid to liquid when heated, and back to solid again when cooled.  Digging deeper into the science, when the glycerin is heated its molecules gain energy, causing them to move around faster. This movement changes how the glycerin molecules are arranged. They become more detached–bonds are broken. At this point the glycerin “melts,” that is, it starts to turn to a liquid state. When it cools, the molecules slow down and bonds reform to create the solid.

Below is a video showing how to make glycerin soap. As in the video, one can add fragrance, flower pieces, and other items (even small toys) to make this product uniquely theirs.

Resources

PBS: Crafts for Kids – Handmade Soaps

PBS: Fish-in-a-Bag Soaps

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