Soap

Soap is an anionic surfactant used in conjunction with water for washing and cleaning that historically comes in solid bars but also in the form of a thick liquid. Soap, consisting of sodium (soda ash) or potassium (potash) salts of fatty acids is obtained by reacting fat with lye in a process known as saponification. The fats are hydrolyzed by the base, yielding alkali salts of fatty acids (crude soap) and glycerol.

Many cleaning agents today are technically not soaps, but detergents, which are less expensive and easier to manufacture. Soaps are useful for cleaning because soap molecules attach readily to both nonpolar molecules (such as grease or oil) and polar molecules (such as water). Although grease will normally adhere to skin or clothing, the soap molecules can attach to it as a "handle" and make it easier to rinse away. Applied to a soiled surface, soapy water effectively holds particles in suspension so the whole of it can be rinsed off with clean water.

The hydrocarbon ("fatty") portion dissolves dirt and oils, while the ionic end makes it soluble in water. Therefore, it allows water to remove normally-insoluble matter by emulsification The most popular soapmaking process today is the cold process method, where fats such as olive oil react with lye. Soapmakers sometimes use the melt and pour process, where a premade soap base is melted and poured in individual molds. While some people think that this is not really soap-making, the Hand Crafted Soap Makers Guild considers it a form of soap making or soap crafting. Some soapers also practice other processes, such as the historical hot process, and make special soaps such as clear soap (glycerin soap), which must be made through the melt-and-pour process.

Handmade soap differs from industrial soap in that, usually, an excess of fat is sometimes used to consume the alkali (superfatting), and in that the glycerin is not removed leaving a naturally moisturising soap and not pure detergent. Superfatted soap, soap which contains excess fat, is more skin-friendly than industrial soap. However, if not properly formulated, superfatted soaps can leave users with a "greasy" feel to their skin. Often, emollients such as jojoba oil or shea butter are added 'at trace' (the point at which the saponification process is sufficiently advanced that the soap has begun to thicken), after most of the oils have saponified, so that they remain unreacted in the finished soap. Superfatting can also be accomplished through a process called superfat discount, where, instead of putting in extra fats, the soap maker puts in less lye.