Soap is used, usually with water, to clean and sanitize helping to prevent disease and infection.
How Soap Works
Soap is made of up of molecules that have one end that is hydrophilic or “water-loving” and another end that is hydrophobic or “water-hating”. The part that hates water mixes well with grease, fat and dirt. The part that loves water mixes well with water. Water and grease would not typically dissolve together but soap grabs a molecule of water on one end and a molecule of grease on the other end and holds them together thereby allowing the water to wash away the grease and other dirt.
Traditional soap making consists of leaching water through the ashes of hard wood in order to produce lye water. Animal fat is rendered and the resulting tallow is boiled with the lye water. A chemical reaction occurs in which the triglycerides, or tallow, and the base, or lye, result in glycerin and soap.
Modern soap making still uses the same chemical process and basic ingredients. Sodium hydroxide is used instead of lye water. Potassium hydroxide can also be used but is less prevalent. Off the shelf oils are used in place of rendering tallow from animal fat. There are a plethora of oils that can be used. You can find several options at any local grocery store including olive oil, canola oil, vegetable oil and coconut oil and a wider variety can be found at specialty stores or upscale grocery stores.
Each oil brings a unique trait to the soap it is used to produce. For instance, coconut oil will produce a soap that lathers well but may dry skin out. Olive oil will produce soap that has a mild lather but is an excellent moisturizer and produces a hard bar of soap. Palm oil produces soap that does not lather much and provides little to no skin moisturizing but cleans well. It’s interesting to note that the ability to cleanse and how well a soap lathers are not necessarily related. Additionally, how soft or hard a soap is refers to physical brittleness and is related to how long a bar of soap lasts but has little to do with how moisturizing a soap is to skin.
As each oil offers different properties most modern soaps are made with a mixture of different oils. Suggested limits and mixtures can be found on many online sources as well as books. One of the most popular modern soap making books is The Soapmaker’s Companion: A Comprehensive Guide with Recipes, Techniques & Know-how by Susan Miller Cavitch. Soap recipes vary widely and different oils cannot be arbitrarily replaced. A recipe is measured based on the specific chemical makeup of each oil involved and how much sodium hydroxide and water is necessary to form a complete chemical reaction. If a specific balance is not achieved you will end up with undissolved fat or lye in your soap. While a certain amount of undissolved fat is good for skin health, undissolved lye can be dangerous. It is important to use recipes from reputable sources.
Additives and Alternatives
In addition to oil and sodium hydroxide some soapmakers use additives including dyes, fragrances, exfoliants such as oatmeal, and moisturizers such as honey. Typically, the sodium hydroxide is dissolved in water but the water can be replaced with other liquids such as goat’s milk or even beer.
An alternative to making soap from scratch is the process of making melt and pour soaps. Many craft stores carry kits that include pre-made soap. A crafter melts the soap, uses additives of his or her choice, and cools the soap, usually in decorative molds.
There are two processes to make modern soap, the Cold Process and the Hot Process. The two processes are almost identical except that the hot process uses additional heat to speed up the saponification. While the chemical reaction may be sped up, the touch time required by the soapmaker is actually greater.
- Choose a recipe. Start out by using tried and true recipes from popular websites and books. When you have gotten comfortable with the soapmaking process it’s time to branch out and create your own recipe. There are websites with calculators that can be used to get the correct ratios and measurements. Never arbitrarily mix oils and lye to make soap without having the correct measurements.
- Gather your personal protective equipment. Working with lye is dangerous and can cause serious chemical burns. Always use gloves. It’s best to use tall gloves that will protect your arms but wrist high gloves and a long sleeve shirt will provide sufficient protection. Always use eye protection. An eruption can occur due to many circumstances including mixing ingredients in the wrong order or using a heat setting too high. It’s very important to protect your eyes.
- Measure your ingredients out. It’s important to be exact. Some items may be measured by weight and some items may be measured by volume. Reputable sources will guide you in this.
- Dissolve the sodium hydroxide in distilled water. Distilled water is important as it doesn’t contain the impurities found in other water sources. Impurities in your soap will cause cloudiness and in some cases odors. Always pour the lye into the water and not the other way around. Pouring water into lye can cause an eruption.
- Mix all of your oils together, melting any oil that is solid.
- Pour your lye mixture into the oil and stir. An emersion blender is a handy tool at this stage and much easier on your than a whisk. If performing the hot process you will maintain a steady heat to the mixture. If using the cold process, turn off all heat sources. In both cases, stir until an emulsion is reached called a trace. There are many online videos available that will help you identify when you have reached this stage.
- In the hot process the mixture will continue to be cooked for a length of time until the gel phase is reached. The cold process will skip this step and go directly to additives.
- Add any additives such as essential oils, fragrances, colorants and exfoliants.
- Pour the soap into molds. Molds can be in the shape of individual bars or a log that requires cutting later.
- Allow the soap to cool down. This typically takes 24-48 hours.
- Unmold the soap. Cut into bars if necessary.
- Cure the soap. Soap is left to air dry for one to two weeks. This gives the soap time to finish any remaining saponification and allows excess water to evaporate. After this stage your soap will be ready to use.
- Sciencebuddies.org - The Chemistry of Clean: Make Your Own Soap to Study Soap Synthesis
- About.com - Saponification
- FragranceX.com - Traditional Soap Making
- ChemistryExplained.com - Soap
- Southern Belle Soaps - Properties of Oils
- HappyNews.com - The difference between cold process, hot process, and melt and pour
- Curious-Soapmaker.com - Cold process vs hot process - which one to choose?
- ThisOldHouse.com - 10 Uses for Soap