Suds Up: How to make soap, 19th-century style

Piqued by the innovation, resourcefulness, and ingenuity required in an era before washing machines did all the scrubbing for us, we decided to make our own soap.

The museum is finalizing preparations for an upcoming summer program, Wash, Rinse, Wring, Repeat!: 19th Century Laundry at Home. Slated to launch June 11, the program will examine the development of laundry technology over time and invite visitors to wash linens using methods unfamiliar in this day and age.

To get us in the nineteenth-century mindset, Christopher Wilson, Director of Daily Programs, guided the staff through saponification (the chemical process of producing soap) as it would have been performed by Americans a century ago. With only a few modifications (e.g., a hot plate rather than an actual fire to heat the animal fat), we produced an unscented batch and another infused with peppermint oil extract.

Take a look at how we saponified to success:

STEP ONE: Collect and melt the fat.

Soap has three main ingredients: fat, lye (sodium hydroxide), and water. It is crucial that these components are precisely measured and kept at appropriate temperatures throughout saponification.

We began by melting large containers of cold animal fat. Many different kinds of fat can be used to make soap, and we chose a combination of leftover bacon grease and drippings from roasted chickens and turkeys—the smell reminded me of Thanksgiving dinner.

Numerous soap recipes can be found on the Internet, but we liked Snowdrift Farm’s website in particular because it allows readers to specify the oil in use.

Here’s Chris explaining the importance of melting points as we melted the fat into oil on a hot plate.

STEP TWO: Combine the lye and water, and bring the mixture to the right temperature.

After melting the fat to the right temperature (we used a chemical thermometer from The Lemelson Center’s Spark!Lab), we determined the weight of the fat (this time, with the help of Spark!Lab’s digital scales). Next, we combined water and lye, and I was surprised by how quickly the temperature rose upon combination.

According to Chris, nineteenth-century Americans had to be careful when adding the lye: too much, and the solution can become very caustic and leave chemical burns on the skin.

Here’s Chris mixing the lye and water.

STEP THREE: Mix all the ingredients together, and let it set for a month.

Once the oil and water/lye combination were all set, Chris brought them together in a bowl using a (decidedly non-period-appropriate) electronic hand mixer. The solution quickly transformed into a thick, light yellow liquid. I can only imagine how tiring the process must have been without the help of a handy electric appliance. We then poured the soap into a container, where it will rest for a few weeks before we kick off our laundry program on the National Mall terrace.

Here’s Chris combining the oil and water/lye solution, and presenting the final product.

Between melting the fat and working with a substance like lye, saponification can be dangerous and cause serious burns if one does not take the appropriate cautionary measures. If you decide to make soap on your own, be sure to wear safety goggles and use heat-resistant gloves like we did.

The saponification lesson made me feel like I was back in school: hearing words like “melting point,” “caustic,” and “chemical reaction” reminded me of the degree to which science can dictate our everyday lives—and even household chores. We hope you come visit the Wash, Rinse, Wring, Repeat! program at the museum this summer, and suds up!

Do you have any science lesson stories to share? Have you ever made soap, or even done laundry without the help of modern machines? Share your thoughts and comments below!

Julia Imbriaco is a seasonal Floor Manager in the Department of Daily Programs.