Most commercially manufactured liquid soaps contain synthetic preservatives and surfactants. Making your own liquid soap gives you the advantage of knowing exactly what you're using on your body, and allows you to adjust the ingredients for specific cleansing needs, or add nutrients to make your soap the best it can be for your skin.
Making potassium-based liquid soaps gives you the versatility of being able to make a whole range of products from one base. These products can include kitchen hand soap, dish soap, laundry liquid soap, facial foam soap, shampoos, bubble baths, shower gels, and more.
Important Caution: Potassium hydroxide is a toxic and caustic chemical, which is usually found in flake form. Like all caustic substances it must be treated with respect. Avoid breathing in the fumes when mixing potassium hydroxide with water. Always use protective rubber gloves when working with potassium hydroxide. Glasses or protective eye covering is also recommended.
More on fats and oils... The fats and oils used in liquid soap making can be grouped into two categories: soft oils and hard oils.
Soft Oils: Soft oils are generally liquid at room temperature and are high in oleic, linoleic, and linolenic fatty acids. These oils include:
Soft oils provide moisturizing benefits to soaps but have less lathering or foaming than soaps made with a combination of hard and soft oils. The exception to this observation is castor bean oil. Castor oil creates a full and rich lather which makes it a valuable addition to liquid soaps used as shampoos.
Hard Oils: The hard oils are generally in a solid/buttery state at normal temperature, including:
The most commonly used hard oil in liquid soaps is coconut oil. Coconut oil contains lauric acid, which makes it very soluble. The more soluble the fatty acid, the less likely you are to have cloudiness in the finished soap. Solubility also contributes to a very quick and heavy lather. This is particularly good for liquid soaps. Soaps high in coconut oil perform well in areas with hard water, even in salt water. In order to avoid the drying effects of lauric acid, it is normal to mix coconut with a range of soft oils, providing the best of both worlds.
Another difference between soft oil soaps and those incorporating a lot of hard oils is the viscosity of the finished product. Coconut-based liquid soaps have the highest actives (cleaning power) and generally have the lightest viscosity (thinness), while soaps using all liquid oils can be thickened somewhat using a variety of different salts, etc. Most of the liquid soaps on the market (ie: Dr Bonners, etc.) use a mix of oils including coconut, and this accounts for the thinness of the finished product. Soaps using hard oil are also much easier and quicker to make (mixing to the paste stage) than soaps using only soft oils.