Cold Process Soap: An Expert Guide to Making It at Home
It's made with a special secret ingredient.
We're ready to let you in on a little secret: The perfect bar of soap is waiting to be yours—all you have to do is make it. Today, homemade soaps can be crafted with the natural, skin-nourishing ingredients your skin needs and deserves. A good cleanser is fundamental to a healthy skin care routine, whether your preference is a heavy-duty oil, a mild soothing cream, or an exfoliating scrub. But with the many options out there on the market, you may be doing yourself a disservice by overlooking the humble bar of soap. If you want to customize a bar of soap down to the last ingredient, consider the cold process method.
Cold process soap is made by combining oils and sodium hydroxide lye, which causes a chemical reaction called saponification. In the process, you get to choose the oils, scents, colorants, and any other ingredients. It's a great way for someone to master the art of soap-making and spa crafts.
Why Cold Process Soap?
It's a time-tested technique: The art of soap-making can be traced as far back as ancient Babylon when archaeologists, during an excavation, first discovered a soap material inside clay cylinders dating as early as 2800 B.C. Inscriptions on the cylinders described a process of fats boiled with ashes, the world's first soap-making method. But the Babylonians weren't the only ones who benefited from this idea. Today, the cold process method of soap-making evolved to rely on a different ingredient called sodium hydroxide or commonly known as lye.
Some of the world's best soap makers use the cold process method. For instance, Savon de marseille was one of the best-kept secrets of southern France, and only in recent history have these artisanal soaps found their way to other parts of the world. Its superb qualities—from olive oil, marine ash, and sea saltwater—are praised for gently nourishing the skin. This is because each ingredient is carefully sourced, and the process controlled from beginning to end.
Similarly for you: A simple but effective soap can be made using a few inexpensive ingredients from your kitchen pantry or homegrown herbs from the garden. Homemade soaps using the cold process method make a great project for using an abundance of aromatic and antibacterial herbs such as rosemary, sage, thyme, and oregano. Roses and lavender add a soft scent while citrus zest adds a zing. The cold process method is ideal for preserving the benefits of plant-derived oils and butter. (The quality of these ingredients can be lost in the melt and pour method.)
First and foremost, you'll need lye, which is a strong chemical that requires utmost caution when handling. For safety, we recommend wearing a pair of goggles, plus rubber or latex gloves with a long-sleeved shirt. Work in a well-ventilated area. Always add lye to liquids (instead of the other way around or it may have a volcanic effect). When mixing lye into liquid, it gets hot quickly and will emit fumes. If you get lye on your skin, rinse with cool water. For burns or eyes, rinse then seek medical attention.
Next, you'll need your oils. Shea butter, argan oil, olive oil, and other ingredients provide a creamy lather for deep moisturizing of the skin. Use the one that is specified in your recipe, or experiment with ones you like. You can also add fragrances and colorants, but we suggesting using organic ingredients and cold-pressed carrier oils to ensure the best quality for your skin. We also advise using them sparingly. Because the soap takes weeks to cure, the scent intensifies over time. To color soap naturally, try clays and botanicals such as French green clay, rose kaolin clay, or indigo powder. Be sure to test the ingredients of your homemade soaps on a small area of your skin first (the inside of your elbow, for example) to make sure that you are not allergic.
A digital scale ($49.95, williams-sonoma.com) is another important tool in soap-making, as this will ensure ingredients are measured precisely, especially lye; otherwise, you may not craft a balanced bar of soap. Additionally, all ingredients should be measured by weight rather than volume, since inconsistent measurements will yield unreliable results. A candy thermometer ($14.95, surlatable.com) works well to measure the temperature of lye solution and oils. We also suggest stocking up on heatproof containers: Use stainless steel, high-density plastic, or enamel-lined or ceramic for mixing water and lye. Aluminum or nonstick surfaces tend to react poorly with lye.
Spoons and spatulas work well for mixing, while a bench scraper or serrated knife will cut your homemade soap into smaller portions. Last but not least, you'll need molds. Use muffin tins, loaf pans, boxes, and cartons, many of which are likely already in your kitchen. Silicone molds for baking work well since you can bend them out of shape to pop out soap shapes. While they have the advantage of being nonstick, they often retain moisture, so keep in mind that homemade soaps may have to rest for a few extra days before being removed.
How to Make Cold Process Soap
This is a base recipe only. The step-by-step instructions of individual projects may vary. Before you begin, assemble your ingredients. If needed, prepare safety gear such as goggles, gloves, and long sleeves. Cover your work surface with newspaper.
First, weigh lye in a heatproof container. Weigh water in a separate container. (Note: A lye calculator is handy here: simply enter the oil weight or percentage, and the tool will provide the lye and liquid amount needed for the recipe.) Next, carefully pour the lye into water, stirring gently with a heatproof utensil until the lye has fully dissolved. Set aside, and let cool for up to an hour. Then, while the lye solution is cooling, weigh oils or solid butters. Melt with a double-boiler until up to 100 degrees.
Next, pour the lye solution into the container of oils. Stir until trace is reached. (Trace refers to the point when the oils and lye solution have emulsified. At this stage, there should be no streaks of oil and the soap will have the consistency of batter.) Then add any extra ingredients—such as natural exfoliants or colorants—stirring to combine. Finally, carefully pour melted soap into the mold. (The soap is still caustic at this stage, so keep your safety gear on when handling.) Cover the mold with a sheet of paper. To retain heat, wrap a towel around it. Set aside for up to two days or until completely cool and solid. When ready, remove homemade soap from the mold and slice into bars. Let the bar soaps cure in the open air for at least four weeks before using.