Soap is a 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, especially from soap dispensers in public washrooms.
Historically, soap has been composed of sodium (soda ash) or potassium (potash) salts of fatty acids derived by reacting fat with lye in a process known as saponification. The fats are hydrolyzed by the base, yielding glycerol and crude soap.
Many cleaning agents today are technically not soaps, but detergents, which are less expensive and easier to manufacture
The most popular soapmaking processes 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 does recognize this as a legitimate 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. Superfatted soap, soap which contains excess fat, is more skin-friendly than industrial soap; though, if not properly formulated, it 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 processed called superfat discount, where, instead of putting in extra fats, the soap maker puts in less lye.
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